Vertical Tabs in Firefox

Published on 2019-05-24.

While other web browsers ship with vertical tabs out-of-the-box, support for vertical tabs is non-existing in Firefox.

Add-ons have failed to deliver a bearable user experience due to a myriad of largely intentional limitations in the Web Extensions API these add-ons are forced to use.

Firefox users have manually adapted the user interface for years by adding changes to their userChrome.css file.

With support for this approach being deprecated and removed, it felt right to use the remaining time to explore whether it’s possible to build an enjoyable user experience with the tools available.


  1. Install the Tree Style Tabs add-on for Firefox.
  2. Go to Firefox’ profile directory, create a chrome directory and create a file named userChrome.css in that directory.
  3. Copy these CSS rules into the file.
  4. Add these CSS rules to Tree Style Tabs’ “extra style rules for sidebar contents” section:
    Add-onsTree Style Tabs PreferencesAdvanced.
  5. Activate Firefox’ bookmark toolbar and right-click into the top left area to add new bookmarks.
    (Specifying a URL, but not a title will turn them into icons.)


Here is the result:

Firefox with vertical tabs