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mozregression is an interactive regression range finder for Mozilla nightly and inbound builds. It uses a binary search algorithm for quickly determining a changeset range corresponding to when a problem was introduced. It is widely use by Mozilla developers and other community members to help find regressions.

To get a feel for how mozregression works, see the video on


Active contributors

These people are actively working on mozregression and good people to ask questions of (or for review):

How to setup for development


Issue / feature tracking

We track mozregression bugs and feature requests inside bugzilla, in the Testing / mozregression component.

Full Query
ID Summary Priority Status
997395 Allow installing addons from a nightly location -- NEW
1084189 Cannot use IME on Nightly builds which are launched by mozregression -- NEW
1192488 mozregression GUI installer needs admin privileges -- NEW
1197106 Add some non regression tests for mozregression -- NEW
1210046 Android builds should always behave the same way when doing A/B testing -- NEW
1217443 using the skip feature is quite confusing -- NEW
1231950 Ship (or use Desktop Fx) Android ADB with mozregression -- NEW
1232037 Output results in machine-readable format (json?) -- NEW
1232877 Option to check a date range prior to a certain build -- NEW
1233339 We may need a panel to show which build has been downloaded -- NEW
1233909 mozregression should go back further than one year for some 64-bit debug js shells -- NEW
1234029 use debug builds from archives.m.o -- ASSIGNED
1235020 [gui] final result log output worthless -- NEW
1235127 [gui] Mozregression sometimes fails to continue bisection in mozilla-inbound builds -- UNCONFIRMED
1235260 [gui] Mozregression incorrectly sets day if I paste date string after selecting text from end to beginning -- REOPENED
1236101 [meta] Bugs that block autoBisect from using mozregression -- NEW
1237057 Have a link to the mozregression-gui.exe binary on the mozregression homepage -- ASSIGNED
1239150 Support dynamic extend reproduce range -- UNCONFIRMED
1239699 print the bugid that is the cause of a regression, probably do more -- ASSIGNED
1241358 [gui] remember "bits" choose, or take the default value ​​from the configuration file -- NEW
1241365 [gui] show ~* steps left on interface -- NEW
1241376 [gui] Progress list should scroll to the last item when it overflows -- NEW
1241380 [GUI] be able to load and display a previous run -- NEW
1241919 HTTP proxy support -- NEW
1245283 mozregression and mozregression-gui aren't using the requested profile on windows 10 -- NEW
1245587 Make Android API changes simpler for mozregression to handle -- NEW
1246086 [gui] Preselect profiles folder when you click on 'browse' -- NEW
1246142 The --pref command line parameter goes silently ignored in some cases -- NEW
1246383 [gui] Mark downloaded package on Build verdict window ('skip' action) -- NEW
1246891 [gui] Allow set days of ApproxPersistChooser in Run a single build -- NEW
1246903 Add a 'go to build...' action to other menu -- UNCONFIRMED
1247061 Reusing connections to improve performance P5 UNCONFIRMED
1248138 [gui] Allow redownload if download is interrupted or "ERROR : Unable to install" -- NEW
1248212 [gui] AssertionError when double click the first/last on Build skipped dialog -- NEW
1248239 [GUI] allow to check the builds of the initial range, as we do in the CLI -- NEW
1248636 [gui] Options description is hard to find in Global preferences -- NEW
1248690 [gui] View the parameters in "Bisecting on" details -- UNCONFIRMED
1248767 [gui] Current build closes after 3 minutes if I restart browser (in different e10s state or with add-ons disabled/enabled) -- NEW
1249737 Mozregression lost when a build fails to start -- NEW
1256317 Error while trying to bisect fennec builds -- NEW
1256379 Automatic bug number selection chose the wrong bug from an inbound range with a backout -- NEW
1256445 mozregression does not allow to execute other mach commands -- NEW
1256974 Mozregression doesn't launch newer Fennec builds -- NEW
1258166 [gui] Support save as default and clear button to custom preferences and custom addons -- UNCONFIRMED
1258688 [gui] Mozregression doesn't store values of some fields ("profile", "search for fix") when I switch back and forth between forms -- NEW
1258831 [gui] Mozregression displays crash error when I try to close single build (clone-first) using X button -- NEW
1260985 Update Linux debug jsshell earliest known working builds to 2015-07-31 -- NEW
1263361 Exception in thread when hitting error ResourceNotFound 404 -- REOPENED
1270893 mozregression "To resume, run..." command goes nuts if it finds nested double/single quotes -- NEW
1275499 TypeError: unsupported operand type(s) for -: '' and 'datetime.datetime' -- NEW
1277888 mozregression --build-type fennec doesn't work -- NEW
1281790 mozregression shouldn't output bug numbers when there are too many possibilities -- NEW
1306661 doesn't recover from temporary interruptions to Internet connection -- UNCONFIRMED
1308028 out of disk space not handled well (ambiguous error, no way to recover or retry) -- UNCONFIRMED
1308417 Mozregression drops bookend integration revisions on the floor -- NEW
1311474 Mozregression fails to run with pkg_resources.DistributionNotFound: colorama -- NEW
1320322 mozregression should know about earliest Thunderbird build -- NEW
1323445 Mozregression should not identify a specific commit if there are multiple commits in the final range -- NEW
1327383 Mozregression GUI doesn't withstand disabling internet connection with background downloads enabled -- NEW
1327595 Mozregression GUI somehow can't subtract date from buildID during bisection -- NEW
1327668 [gui] If I doubleclick on "Bad" button in Mozregression - it marks BOTH builds as bad -- NEW
1327669 [gui] It's possible to accidentally start background download after quick cancellation -- NEW
1334853 mozregression --launch BUILDID used near-build instead of exact -- UNCONFIRMED
1334856 mozregression can't handle restarted firefox -- UNCONFIRMED
1339492 Mozregression fails to launch OSX builds older than 2016-07-12 -- NEW
1350527 DownloadInterrupt should be processed -- NEW
1350530 'Retest' button on past items -- NEW
1351290 Bisecting mozilla-release with dates 2016-03-19 -> 2017-03-19 doesn't seem to work on (at least) win32 -- NEW
1362127 Add option for just getting commit range for two dates without downloading / testing builds -- NEW
1365479 [gui] List recent used downloaded builds for Run a single build -- NEW
1366570 mozregression installers for windows and mac are not signed -- NEW
1381319 [gui] Unreadable text depending on system theme -- UNCONFIRMED
1394911 Add option to not launch Firefox -- NEW
1394919 Add option to download binaries from final release -- NEW
1395905 Allow reusing builds which were used recently -- NEW
1398903 Provide standalone APK version of mozregression GUI and mozregression for Android -- NEW
1401503 Launcher error in mozregression GUI 0.9.13 -- NEW
1401649 Make mozregression work with localized builds -- ASSIGNED
1407089 Add support for reading prefs from a JS file -- NEW
1407430 Unable to find regression range between two specific date -- NEW
1408696 mozregression can't verify the revisions it itself produced -- NEW
1422117 Crash during bissection process -- UNCONFIRMED
1427371 mozregression just ran entirely the wrong build for me! -- NEW
1439887 On small initial window, input verification is skipped -- NEW
1449899 Issues installing on macOS -- NEW
1458834 Retrying a build takes ages -- NEW
1460596 [gui] Ability to save bisection session & log -- NEW
1465145 bisecting API 11 fennec on API15 Android devices isn't working -- UNCONFIRMED
1470495 Clean up obsolete branches and add some other ones -- NEW
1477781 Incorrect regression range points to wrong bug -- ASSIGNED
1477784 "Bisection informations" should say "Bisection information" -- NEW
1478217 Bisection stuck in infinite loop -- NEW
1484381 "A new Nightly update is available" door hanger when mozregression is running builds -- NEW
1484531 mozregression cannot find/use OpenSSL ( -- UNCONFIRMED
1484533 Provide virtualenv for cli -- UNCONFIRMED
1485981 Mozregression for x86 devices -- NEW
1487262 mozregression only outputs the topmost commit in a push. -- NEW
1488907 Unexplained long pause before launching a Firefox instance -- NEW
1499595 add option for downloading in background -- NEW
1500653 Fennec crashes immediately when installed via mozregression -- NEW
1502956 Test changeset for regression -- NEW
1503358 mozregression-gui crash: LookupError: no codec search functions registered: can't find encoding -- NEW
1504259 Trying to use mozregression with Fennec results in "Permission denied" error -- NEW
1519138 mozregression-gui: revise the last decision -- UNCONFIRMED
1520789 Binary path is not getting escaped -- NEW
1524066 --profile-persistence={clone-first,reuse} do not work on Android -- NEW
1525283 Please make it possible to resume failed downloads -- UNCONFIRMED
1536324 Errors running mozregression on Windows P3 NEW
1544735 Firefox is crashing with builds from around the 2017-07-19 P3 NEW
1548014 mozgregression --arg doesn't work with --app=jsshell P3 NEW
1550806 "Unable to start the application" when attempting a bisection when parent.lock in profile P3 REOPENED
1556042 Support Fenix as an app in mozregression P3 NEW
1558462 jsshell doesn't support testing functions P3 NEW
1566835 [gui] Add keyboard shortcuts for menu items -- ASSIGNED
1568086 Provide switch to pull only nightly builds/official signed builds -- NEW
1568488 Mozregression support for Firefox Reality browser -- NEW
1570650 mozregression should work with esr branches -- ASSIGNED
1580625 `mach mozregression` should install mozregression into its own dedicated virtualenv P3 NEW
1581643 Provide standalone mozregression-gui builds on Linux again -- NEW
1602976 How to bisect list of installed extensions to find which is responsible for a bug? -- UNCONFIRMED
1604963 Attach mozregression log to related bug -- NEW
1604965 Allow mozregression to select the range based on a bug in Bugzilla -- NEW
1604967 Mozregression could set the 'Regressed By' field if a specific commit was found -- NEW
1604969 mozregression could run test cases added to bugs -- NEW
1610427 Mozregression should not look for taskcluster builds more than 1 year old P3 NEW
1615667 mozregression buries its actionable output behind pages of warning-spew, for ranges that are too old for intermediate taskcluster builds P3 NEW
1622953 mozregression warns about soupsieve not being installed on startup P3 NEW
1622958 Add a way to specify environment variables on Android -- NEW
1627626 mozregression cannot be installed on mac os 10.12 P3 NEW
1629603 Improve docs/walkthrough for mozregression on MacOs -- NEW
1631163 Updated notification is wrong when mozregression runs from repo P4 UNCONFIRMED
1631167 mozregression GUI does not sanity check user-specified good/bad builds P4 UNCONFIRMED
1637164 Crash RuntimeError: dictionary changed size during iteration -- UNCONFIRMED
1639571 Prevent selecting date before 2004-12 -- NEW

134 Total; 134 Open (100%); 0 Resolved (0%); 0 Verified (0%);

Submitting patches

If a bug is not open already corresponding to the bug you want to fix (or the feature you want to add), please file one. After that, please open a github pull request with your code change, and set a flag in bugzilla for it to be reviewed, as described here:

Please make sure your patch conforms to PEP8 before submitting it.