What is Firefox Nightly?
Every day, Mozilla developers write code that is merged into a common code repository (mozilla-central) and every day that code is compiled so as to create a pre-release version of Firefox based on this code for testing purposes, this is what we call a Nightly build. Once this code matures, it is merged into the Beta stabilization repository where that code will be polished until we reach a level of quality that allows us to ship a new final version of Firefox to hundreds of millions of people. This development process used to ship a new version of Firefox every 4 weeks is called the Train Model.
Should I become a Nightly user?
Of course, Nightly does not have the polish, quality and stability of the Release channel as this is a work in progress but we are doing our best through automation, QA and community to provide you the best nightly builds possible.
If you are a power-user, that you want to have access to features in developments months or years before they become mainstream, have tolerance for occasional functional regressions and are looking for an easy way to help Mozilla and Firefox development, you should use Nightly (ideally as your main browser but you can also use it alongside Firefox on the release channel or another browser).
Unlike Firefox on the Release channel, Nightly sends by default anonymized usage statistics, called Telemetry which helps us improve Firefox and track regressions on a daily basis. Just using Nightly and sending telemetry data is already of great help to all Mozilla developers as it allows them to get usage statistics on the features they work on.
Of course, Nightly may be more likely to crash than a final release and sending your crashes to our engineers is also of considerable help as it helps us catch instabilities and identify issues long before end-users are exposed to them.
And if you want to go a step further, you can file bugs in our Bug tracker with detailed information about what is not working for you in Nightly.
Where can I download Firefox Nightly?
➡ Go to nightly.mozilla.org
Nightly is available for all the platforms we support officially (Windows 7 and later, MacOS, Linux) and we provide both 32 and 64 bits for Linux and Windows. We also support a large range of languages ranging from Albanian to Vietnamese.
All of our available builds are listed on this page: https://www.mozilla.org/firefox/nightly/all/
How does it update? Update interval?
Nightly gets an update twice a day (or night, depending on your timezone), building starts at 10:00 and 22:00 UTC, usually builds are available one hour or two later. That means that there is an update in the morning for The Americas and another one for EMEA/Asia
The update is downloaded in the background, when this is done, there is a small green badge that appears on the hamburger menu which indicates that if you restart your Nightly, an update will be applied.
If you don't apply this update within 12 hours, a dialog box will pop up asking you to do so. If you want this dialog to show up later than 12h, in about:config change the app.update.promptWaitTime value from 43200 to a higher value, 86400 for 24 hours for example.
Sometimes, we will issue more than two updates per day, typically this is because we found out we introduced a major regression (a spike in crashes for example) and we don't want our users to have a broken browser for 24h.
Sometimes we will have only one nightly or no nightly if there are no patches landed or if we think that the quality is not good enough.
My nightly build is broken and can't update to a newer Nightly
On very rare occasions, Nightly can suffer from a bad regression making it totally unusable or unable to receive updates.
If you are stuck on an unusable nightly or if you stopped receiving automated updates, the solution is to download and reinstall a newer Nightly build from nightly.mozilla.org.
Where can I get news about Nightly?
We maintain a few communication channels to give you news about the development of Nightly features or activities relevant to our community of Nightly users:
- Twitter: https://twitter.com/FirefoxNightly
- Blog: https://blog.nightly.mozilla.org
- Matrix channel: #nightly on chat.mozilla.org
- Experimental platform features page on MDN: https://developer.mozilla.org/en-US/Firefox/Experimental_features
- Release notes (updated every week): https://www.mozilla.org/en-US/firefox/nightly/notes/
- Nightly category in our Mozilla Community Forums: https://discourse.mozilla-community.org/c/nightly
This activity has great potential to make an impact by increasing overall involvement in Nightly, simply by introducing community to tasks that they can engage in related to Nightly. Finding and filing issues early in the cycle means by the time Firefox gets to release, the code is in good shape.
- Mozilla Activate: https://activate.mozilla.community/nightly/
I found a bug, how do I report it?
First of all, thank you for doing that! Bugs reported early are also more easy to fix or back out than bugs reported weeks or months after the code was written, simply because developers just wrote it and have all of it fresh in their memory.
If you think you have found a bug in Nightly, the best thing to do is indeed to report it in our Bug tracking system, called Bugzilla.
Bugzilla can be a bit intimidating when you use it for the first time, but we have documentation to help you make useful bug reports here that may get you started: Bugzilla: Bug writing guidelines
Note that you can use a GitHub account to log in to Bugzilla.
Don't hesitate to ask experienced Nightly users (staff or employees) to help you file the bug in the #nightly channel on Matrix if you are unsure about the process or if English is not your native language and want to make sure your bug description is understandable.
Once you have filed the bug, you may get questions from bug triagers (people that enrich existing bug reports with useful metadata and try to get the right dev in front of the right issue) or developers that are trying to reproduce your bug using your configuration or the steps to reproduce what you experienced - watch your mailbox for such messages!
The bug I found is a regression!
A regression is when something that used to work is no longer working or no longer working as expected. If your bug is a regression, please add the regression keyword to your bug report.
We have a specific tool helping us to find when the code that introduced a regression landed in Nightly, this is called mozegression.
There is a GUI for Windows and a command line interface for Linux/Mac.
- Article about the CLI version: Found a regression in Firefox? Give us details with mozregression!
- Article with a video tutorial about the Windows version: Using mozregression on Windows
I want to report a website that doesn't work in Firefox
Some websites do not work in Firefox not because of a Firefox bug but because the site is restricting (intentionally or not) their audience to users of a specific browser. This is what we call a Web Compatibility issue. Since these issues can also affect other browsers than Firefox, web compatibility reports are filed in a separate bug tracker at https://webcompat.com/
There is a special menu item in Firefox Nightly to easily report the site you are visiting as being incompatible with Firefox. Click on the "Report Site Issue" item in the Help menu.
What is the Nightly Tester Tools extension?
This is a useful extension which adds many tools dedicated to bug filing and regression finding.
You can find it on addons.mozilla.org: Nightly Tester Tools
The Github repository has a short description of what it can do.
I found a bug and I want to write the patch myself!
This is a great way to get involved, our developers have full documentation on how to get started hacking on Mozilla code there:
Platform specific instructions
Firefox does not support downgrades, even though this may have worked in past versions. If you install Firefox Nightly and later downgrade to an earlier version, you may experience issues with Firefox if they share the same profile of data.
You will find below additional OS specific instructions as well as a video tutorial for Windows.
How do I install Firefox Nightly alongside Firefox Release?
Here is a video tutorial explaining how to install Firefox Nightly on Windows alongside an existing installation of Firefox: Install Firefox Nightly cleanly on Windows
How do I install Firefox Nightly alongside Firefox Release?
Download Firefox Nightly. As for any Mac OS app, open it either from Firefox or by double-clicking it in the folder, then drag and drop the icon into the application folder and you're done for the installation part. For detailed instructions, see here.
Why is Nightly provided as a tar.bz2 archive? Do I have to compile it?
We build and provide distribution-neutral binaries and these binaries can be installed and updated without any dependency to a package manager.
You don't have to compile anything, just unarchive the tar.bz2 file into your /home or your /opt folder if you want to make it available to all the accounts on your machine and launch the firefox file from your shell. If you decide to install Firefox Nightly outside of your Home, such as in /opt/firefoxnightly, don't forget to give this folder the same rights as your user otherwise it won't auto-update:
sudo chown -R $USER:$USER /opt/firefoxnightly
If you want to create a Launcher for your app, you will need to create a .desktop file, here is on our blog an article about it for Ubuntu and Unity: Getting Firefox Nightly to stick to Ubuntu’s Unity Dock
Is Nightly available as a .deb/.rpm?
As of October 2023, we now officially provide a .deb repository for Debian-based distros (example: Ubuntu, Debian, Mint, etc). See:
Mozilla does not provide yet .rpm packages but our tar.bz2 binaries work on all distributions which meet Firefox system requirements.
Is there a Nightly repository for my distro?
We only maintain a repository for Debian-based distros (see section above)
Some volunteers maintain their own repository or ppa but usually those are not maintained over time for Nightly.
For non-Debian distros, the advised installation method is to use Mozilla-provided builds and its software updater.
Is there a FlatPak/Snap package
Canonical provides Snap binaries of Firefox and will probably propose also them for Nightly at some point, but this is not yet the case. The tracking bug is Automate generation of Firefox snap packages.
We support FlatPack for Beta builds (since Firefox 75) but not for Nightly builds yet.
There is an unofficial Firefox Flatpak repository created by the Fedora/RedHat maintainers for testing purposes: https://firefox-flatpak.mojefedora.cz/
With this FlatPak repository, your profile is stored in
If you are on Ubuntu, here is a detailed article on how to install it here: How to Install Firefox Nightly as a Flatpak App on Ubuntu
Promoting Nightly in your community
If Open Source guerrilla community marketing is something you would like to get involved with and Nightly works great for you, maybe you could promote it to other power-users in your personal or professional networks, getting more users across the globe would help us catch more regressions, get more technical feedback and would allow us to ship a better browser.
There are many ways you can get help at the local level or online.
Some of them are very easy, such as retweeting interesting tweets from our @FirefoxNightly or sharing them on other social networks, some represent more work such as participating to a local open source convention and presenting Nightly or organizing QA activities through Nightly via your local Mozilla community or Mozilla Club.
If you want to present Nightly at an event, please read this blog report: Fosdem 2017 Nightly slides and video
The slides in this presentation are online and can be used as a basis for your own presentation.