Performance Triage

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To (re)nominate a bug for triage, set the Performance Impact flag in Bugzilla to ?

This can be found by clicking Show Advanced Fields followed by Set bug flags when entering a new bug:

Bugzilla performance nomination on new bug form.png

Or by expanding the Tracking section when editing an existing bug:

Screenshot 2022-02-24 at 19.53.54.png


To nominate a bug for triage, add the Performance label to an issue. This can be done by filing an new issue with the "Performance issue" template:

Screenshot of file a "Performance issue" template on GitHub

Or by opening an existing issue on GitHub and selecting the label from the right-hand bar:

Screenshot of adding a performance label on GitHub

Currently, only the following GitHub repositories are supported:


Performance triage

Full Query
ID Summary Status
951052 Improve performance on hixie's element insertion microbenchmark on Android NEW
1694048 Reddit Become Slower NEW
1707386 Intermittent /resource-timing/object-not-found-after-cross-origin-redirect.html | There should be one entry. - assert_equals: There should be one entry. expected 1 but got 0 REOPENED
1745884 Intermittent /user-timing/measure_navigation_timing.html | window.performance.getEntriesByName("measure_nav_start_no_end")[0].duration is approximately correct (up to 20ms difference allowed) - assert_true: window.performance.getEntriesByName("measure_nav REOPENED
1771530 After updating to Firefox 100.0.2 launching the app causes a delay in accessing sites due to 8x iterations running. WIN7 with current updates checking with Task Manager. Seems to create additional instances when other tabs are created.. UNCONFIRMED
1772473 Periodic hangs lasting 5 to 30 minutes on any Windows 10 computer. I've searched bug lists. I don't see it. I've killed background tasks, that doesn't help. Has Microsoft killed Firefox? I was forced to migrate to Edge. UNCONFIRMED
1772903 GetLoadedModulesRunnable slow at shutdown NEW
1774890 Firefox freezes whenever I turn on and connect anothre device to the mobile hotspot on my computer NEW
1780729 main process randomly using 100% cpu UNCONFIRMED
1785046 "Save as PDF" hangs the browser when file-to-be-saved is on virtual disk UNCONFIRMED
1786040 Lots of jank on due to large number of video elements NEW
1788190 Firefox suddenly uses 7.4 GB of RAM with only 4 tabs open (Macbook Pro M1) UNCONFIRMED
1788222 Flatpak Firefox hangs at launch when no global network access UNCONFIRMED
1788853 Slow shut down UNCONFIRMED
1789092 Intermittent FileNotFoundError: [Errno 2] No such file or directory: './resource-timing/resources/importer.js' NEW
1789119 Firefox becomes visually unresponsive while scrolling down a webpage and does not recover UNCONFIRMED
1789146 excess consumption of firefox when closing. UNCONFIRMED
1789190 Intermittent /resource-timing/no-entries-for-cross-origin-css-fetched.sub.html | single tracking bug NEW
1789268 DrawSurfaceWithShadow in canvas is very slow NEW
1789850 Reduce first-startup.timeout from 30 seconds to something reasonable NEW
1790262 high energy usage on mac m1 UNCONFIRMED
1790640 Memory Leakage UNCONFIRMED
1790897 Jank when scrolling Olive Garden menu NEW
1790906 Identify cause of temporary 262ms improvement to Firefox Focus start up & try to ship it to users NEW
1791344 Firefox tab crashes with unclear error message when a lot of memory is used UNCONFIRMED
1791491 pages slow to load UNCONFIRMED
1792133 Intermittent FileNotFoundError: [Errno 2] No such file or directory: '/home/cltbld/tasks/task_166390411536200/build/blobber_upload_dir/browsertime-results/cnn/profiling/pages/www_cnn_com/2021/03/22/weather/climate-change-warm-waters-lake-michigan/ NEW
1792150 Firefox Doesn't loads pages for some time after fresh OS session UNCONFIRMED
1792286 firefox slow to render initial page when first started UNCONFIRMED
1792738 Memory leak with the latest version of Firefox UNCONFIRMED

30 Total; 30 Open (100%); 0 Resolved (0%); 0 Verified (0%);

Performance triage (pending needinfo)

Full Query
ID Summary Status
1371641 YouTube navigation start profile NEW
1492667 Investigate long load time of NEW
1580582 Leaving Twitter open degrades performance of entire browser and causes shutdown hang NEW
1592271 High idle CPU use on Linux (Solus) after latest (70.0) update UNCONFIRMED
1612758 Firefox severely freezing often on scroll UNCONFIRMED
1615046 Google Voice frequently becomes non-responsive NEW
1615369 Performance metrics Round 2 for GeckoView streaming ASSIGNED
1622317 Enormous cooling fan speed when firefox is launched UNCONFIRMED
1645561 High CPU usage during display sleep UNCONFIRMED
1646600 Firefox becomes unusable while on a zoom call under mysterious circumstances NEW
1654087 slow page performance after scrolling through a lot of pages NEW
1654980 Extreme performance degradation in Firefox 78.0 UNCONFIRMED
1658443 windows10 accessing extra files in browser_startup_mainthreadio.js and related tests NEW
1692377 Firefox becomes really show when saving file UNCONFIRMED
1693219 Firefox 78.7 ESR takes a long time to recover after being SIGSTOPped for some time UNCONFIRMED
1700505 45% main process CPU use with web content processes at 15% or less NEW
1700945 Periodic >100% CPU spikes of Firefox when machine is in sleep mode NEW
1725629 Menuitem lags in Bookmarks menu UNCONFIRMED
1753475 Confluence page freezes, huge memory usage spike UNCONFIRMED
1756368 Need to load tabs in smaller batches - Firefox loads individual tabs super quickly, but chokes and shows slow performance when trying to load multiple tabs simultaneously (affects add-ons like STG and possibly startup performance) UNCONFIRMED
1757077 Firefox starts consuming >10GB RAM when idle UNCONFIRMED
1757312 Low frame rate on UNCONFIRMED
1758047 Mozilla Firefox consumes high Background CPU and Memory Usage compared to other browsers UNCONFIRMED
1758082 High resource usage in Gmail UNCONFIRMED
1760785 Firefox is using a high amount of memory, & is showing multiple instances of the app running in Task Manager (more than actual), Memory used in Firefox task manager different to PC Task Manager UNCONFIRMED
1761461 Firefox high CPU use and crash at exit ("shutdownhang") UNCONFIRMED
1763279 SessionStore keeps copying all data into a huge array ASSIGNED
1763724 Firefox excessive battery drain on MacBook (apple silicone) UNCONFIRMED
1764558 Firefox process use excessive amount of memory UNCONFIRMED
1766863 Time from startup to usable tabs extremely long UNCONFIRMED
1768357 Javascript completely halts after 20220506 (or 0507) update UNCONFIRMED
1769108 After I updated to 100.0 (64-bit) google searches slows down my PC for a few seconds and Firefox freezes. UNCONFIRMED
1769763 Massive memory use in structured-clone-holder UNCONFIRMED
1770014 For the last 1-2 weeks Firefox has started locking up after a few hours of use. UNCONFIRMED
1770891 Page do not load, firefox freeze, do not respond but also give no error UNCONFIRMED
1771612 EXCEPTION_BREAKPOINT @ OOM | large | mozalloc_abort UNCONFIRMED
1772139 My browser crashes all the time, but what's going on? UNCONFIRMED
1772249 Jank and checkerboarding when scrolling NEW
1772429 Remove or update probes expiring in Firefox 104: CONTENT_PROCESS_* ASSIGNED
1773804 google sheets eats unusal amount of memory UNCONFIRMED
1774616 FF freezing while shopping online UNCONFIRMED
1775395 Uses most of my memory UNCONFIRMED
1776567 Refreshing Youtube Subscriptions page freezes browser's UI NEW
1778242 Firefox CP Web content taking up a lot of RAM UNCONFIRMED
1781069 A lag when downloading multiple short (<50 MB) videos one at a time on Linux platform UNCONFIRMED
1781105 Excessive RAM usage by FirefoxCP Isolated Web Content UNCONFIRMED
1782845 firefox loads to the point that tab titles show (with no page content) then immediately crashes. UNCONFIRMED
1784501 High CPU & mem usage after >~2 days of usage (no add-ons; "MainThread" prob) UNCONFIRMED
1786940 firefox 104.0 excessive cpu usage UNCONFIRMED
1787957 High CPU & Freeze w/Bitwarden copy NEW
1789852 Figure out alternatives to Nimbus' utilization of the FirstStartup component NEW

51 Total; 51 Open (100%); 0 Resolved (0%); 0 Verified (0%);

Recently opened bugs with performance keywords in the summary

Full Query
ID Summary Status
1791655 Slow performance using PAC with unavailable PROXY and switching to DIRECT NEW
1791730 Remove MemoryOutputStream ASSIGNED
1791806 Hit MOZ_CRASH(attempt to add with overflow) at /third_party/rust/wgpu-core/src/command/ NEW
1791809 Hit MOZ_CRASH(attempt to multiply with overflow) at /third_party/rust/wgpu-core/src/command/ NEW
1791881 Hit MOZ_CRASH(Buffer already dropped.) at gfx/wgpu_bindings/src/ NEW
1791883 Assertion failure: IsAncestorFrameCrossDocInProcess(aAncestor.mFrame, aFrame) (Fix the caller), at /layout/base/nsLayoutUtils.cpp:2601 NEW
1792541 ODoH memory leak when internet connection lost in TRR-only mode, infinite loop trying to update ODoHConfigs. ASSIGNED
1792560 [fission] Transformed (translated) frame contents are blurry since fission isolation NEW
1792634 On flaky/slow connection, if you search with "? search-term" in address bar and reattempt the load, you can end up searching for your search URL instead of your search term ASSIGNED
1792703 Login is not performed on with ETP - Strict enabled NEW
1792797 regression break Asana / Slack floating button NEW
1792831 Hit MOZ_CRASH(called `Result::unwrap()` on an `Err` value: Custom("Invalid bits for ColorWrites")) at gfx/wgpu_bindings/src/ NEW
1792960 Assertion failure: cx->runtime()->hadOutOfMemory, at /js/src/shell/js.cpp:5694 ASSIGNED
1792998 [wpt-sync] Sync PR 36076 - Limit fast-path transform updates to just transform property changes NEW
1793017 Scrolling a Google Doc with an increased page zoom level is slower and jankier than without zoom NEW
1793132 App links performs packageManager query on main thread on every page load NEW
1793147 Assert that network calls are performed off the main thread NEW
1793153 OutOfMemoryError at HttpIconLoaderKt.toIconLoaderResult NEW
1793231 Crash in [@ java.lang.OutOfMemoryError: at<init>(] NEW
1793282 Pinch-zooming a codepen demo leads to a extended period of high CPU use (and may lead to eventual crash) NEW

20 Total; 20 Open (100%); 0 Resolved (0%); 0 Verified (0%);

Triage process


The goal of performance triage is to identify the extent to which bugs impact the performance of our products, and to move these bugs towards an actionable state. The goal is not to diagnose or fix bugs during triage. We triage bugs that have been nominated for triage and bugs in the Core::Performance component that do not have the performance impact project flag set.

During triage we may do any/all of the following:

  • Request further information from the reporter (such as a profile)
  • Set the performance impact project flag
  • Add performance keywords
  • Move the bug to a more appropriate component

Who is responsible for triage?

Everyone is welcome to take part in triage. By default, everyone on the performance team is enrolled in triage rotation, but we also have participants from outside the team.

How do I schedule a triage meeting?

If you are on triage duty, you will receive an invitation as a reminder to schedule the triage meeting on the shared performance calendar with the nominated sheriffs invited at a time that works for them. The responsibility of scheduling the meeting falls to the lead sheriff. Once a triage meeting has been scheduled, it’s a good idea to remove the reminder event from the calendar to avoid confusion. It’s a good idea to use the shared calendar, as this increases the visibility of the performance triage and allows other members of the team to contribute or observe the process.

What if a sheriff is unavailable?

The rotation script is not perfect, and doesn’t know when people are on PTO or otherwise unavailable. If the lead sheriff is available, it is their responsibility to either schedule the triage with the remaining available sheriff or to identify a suitable substitute for the unavailable sheriff(s). If the lead sheriff is unavailable, this responsibility passes onto the remaining available sheriffs.

How do I run a triage meeting?

The following describes the triage process to follow during the meeting:

  1. Ask if others would prefer you to share your screen. This can be especially helpful for those new to triage.
  2. Open the first triage query to show bugs nominated for triage or in the Core::Performance component without the performance impact project flag set. The bugs are sorted from oldest to newest. For each bug in the list, follow these steps:
  3. Open the second triage query to show bugs that have open needinfo requests. The bugs are sorted from oldest to newest. For each bug in the list, follow these steps:
    • If the needinfo was set less than 2 weeks ago, move onto the next bug.
    • If the needinfo was set more than 2 weeks ago but less than 2 months ago, consider adding a needinfo for either: another reporter of the issue, someone with access to the appropriate platform(s) to attempt to reproduce the issue, or a relevant subject matter expert.
    • If the open needinfo was set more than 2 months ago, close the bug as inactive. You can modify the inactive bug template as needed.
  4. If time permits, open the third triage query to show recently opened bugs with performance related keywords in the summary. If any of these look like performance bugs, they can either be triaged the same way as bugs in the initial query or they can be nominated for triage in a subsequent meeting.

How do I determine the performance impact project flag?

The performance impact project flag is used to indicate a bug’s relationship to the performance of our products. It can be applied to all bugs, and not only defects. The triage calculator should be used to help determine the most appropriate value for this flag. In addition to setting the performance impact project flag, make sure to use the “Copy Bugzilla Comment” button and paste this as a comment on the bug.

How do I determine the performance keywords?

There are several performance related keywords, which can be helpful to understand how our performance issues are distributed, or whenever there’s a concerted effort to improve a particular aspect of our products. The triage calculator may recommend keywords to set, and by typing “perf:” in the keywords field in Bugzilla, you will see the available options. Select all that apply to the bug.

How do I determine the correct Bugzilla component?

Ideally we would only have bugs in the Core::Performance component that are the responsibility of the engineers in the performance team. For performance bugs to have the best chance of being fixed, it's important to assign them to the correct component. In some cases the correct component will be obvious from the bug summary, description, or steps to reproduce. In other cases, you may need to do a bit more work to identify the component. For example, if there's a profile associated with the bug, you could see where the majority of time is being spent using the category annotations.

Triage calculator

The Performance Impact Calculator was developed to assist in identifying and applying the performance impact project flag and performance keywords consistently. If you have feedback or would like to suggest changes to this tool, please share these in the #perf-triage Matrix channel.

Triage rotation

The sheriffs are allocated on a weekly basis, which is published here. The rotation is generated by this script.


New bug

This template is included in the description for new bugs opened in the Core::Performance component. If a bug is opened in another component and then moved to Core::Performance, this template can be used as needed to request additional information from the reporter.

### Basic information

Steps to Reproduce:

Expected Results:

Actual Results:


### Performance recording (profile)

Profile URL:
(If this report is about slow performance or high CPU usage, please capture a performance profile by following the instructions at Then upload the profile and insert the link here.)

#### System configuration:

OS version:
GPU model:
Number of cores: 
Amount of memory (RAM): 

### More information

Please consider attaching the following information after filing this bug, if relevant:

 - Screenshot / screen recording
 - Anonymized about:memory dump, for issues with memory usage
 - Troubleshooting information: Go to about:support, click "Copy text to clipboard", paste it to a file, save it, and attach the file here.


Thanks so much for your help.

Moved to Core::Performance

This bug was moved into the Performance component. Reporter, could you make sure the following information is on this bug?

 - For slowness or high CPU usage, capture a profile with , upload it and share the link here.
 - For memory usage issues, capture a memory dump from about:memory and attach it to this bug.
 - Troubleshooting information: Go to about:support, click "Copy raw data to clipboard", paste it into a file, save it, and attach the file here.

Thank you.

No longer able to reproduce

This bug doesn’t seem to happen anymore in current versions of Firefox. Please reopen or file a new bug if you see it again.

No response from reporter

With no answer from the reporter, we don’t have enough data to reproduce and/or fix this issue. Please reopen or file a new bug with more information if you see it again.

Expected behaviour

This is expected behavior. Please reopen or file a new bug if you think otherwise.

Website issue

According to the investigation, this is a website issue. Please reopen or file a new bug if you think otherwise.