This article describes the installation of Stylus for testing purpose. See releases on the main page for permanent installation.

• BACK UP YOUR STYLES before you begin or you may lose them.
• Download:
  • Nightly test builds that may contain severe bugs
  • Released builds that we upload to Chrome web store or Mozilla addons.
• Install in Chrome.
• Install in Firefox:
  • Temporary installation.
  • Semi-permanent installation.

Downloading requires a github.com account.

1. open https://github.com/openstyles/stylus/actions/workflows/ci.yml
2. open an entry and download the build listed in Artifacts e.g. stylus-chrome-mv3-3.0.7-fc0999b is a ManifestV3 build for Chrome/Chromium 128 or newer, fc0999b is the commit hash.

1. Open the menu -> Extensions -> Manage, which opens chrome://extensions page.

2. Check the Developer mode checkbox at the top.

3. In modern Chrome simply drag'n'drop the zip file into that page.

   In some Chromium-based browsers and older Chrome you'll need to unpack the zip file first, click Load unpacked button, select the extracted folder (in newer Chrome it's shown as empty, which is fine), and click "OK".

4. Disable any other versions of Stylus that are already installed!

• Open the following URL: about:debugging#addons

• Click the "Load Temporary Add-on" button (1).

• Select the extracted "stylus" folder (2).

• Select any file within the folder (3). Any file will work.

• Click "Open" (4).

  

• If you already had a permanently installed Stylus from Mozilla addons, it'll be temporarily hidden and will be restored when you restart the browser. Don't remove the extension. Both extensions use the same data.

• Also see Mozilla's video .

To install Stylus in Firefox without needing to follow the above steps every time you load Firefox:

• This won't work with the standard version of Firefox. It has been known to work on Developer Edition, Nightly , and LibreWolf . If you try another edition or fork, please edit this page to mention it.

• Now zip up all of the contents of the stylus folder. Don't zip the folder itself; instead go into the folder, select everything, and zip all of it.

• Go to the Firefox about:addons page.

• Click the gear icon at the top of the page, and choose "Install Add-on From File..."

  

• Select the zip file you just made, and click "Open."

• If you get a message saying that the add-on could not be installed because it appears to be corrupt, then you've made a mistake in downloading, unzipping, and rezipping the extension. Again: the zip file should contain a bunch of files and folders; it should not contain a folder that contains those files and folders.

• If you get a message saying that the add-on could not be installed because it's not verified, then go to about:config, search for xpinstall.signatures.required, and set it to false. Then try installing from file again. If you get the same error message, then you're out of luck for that edition of Firefox.