I have Firefox Quantum web-browser version 57.0.2 (64-bit) in Windows 7.

The Sidebar, unfortunately, has a maximum width of about 540 pixels.

I tried to increase this constraint by going to about:config and searching for "sidebar". Then I changed the setting devtools.toolbox.sidebar.width;500 to a value of 600. Then I restarted Firefox. But it did not work.

So how can I increase the maximum width of the sidebar?

3 Answers 3

  1. Firefox menu -> Help -> Troubleshooting Information -> Profile folder -> Open folder

  2. There should be folder named chrome (all lowercased). If it's missing, create it.

  3. In said chrome folder, there's userChrome.css file. If it does not exist, create it.

  4. Open this file with any text editor.

  5. In this file, if there is no CSS rule #sidebar, create it:

/* remove maximum/minimum width restriction of sidebar */
#sidebar-box {
  max-width: none !important;
  min-width: 0px !important;
  1. Restart Firefox
  • Confirmed in FF 66: No config settings work, but this method does. No way to improve it.
    – u2n
    May 2, 2019 at 19:16
  • Did not work on FF 70.0.1. Nov 12, 2019 at 15:46
  • 6
    Since version 69 and later, Firefox does not load userChrome.css by default. To make it effective again, open about:config in Firefox and set the preference toolkit.legacyUserProfileCustomizations.stylesheets to true
    – mini
    Nov 29, 2019 at 8:42
  • 1
    How do you guys know all of this stuff wth?
    – 55 Cancri
    Jun 28, 2020 at 13:49
  • 1
    Since version 107.0.1, there's a new name to the css property. Thank you @overcast75 for the updated note. Now it should be #sidebar-box. I added the new property into the css file, restarted and it worked. Dec 7, 2022 at 7:10

Looks like this tag has had its name changed recently. The new tag is:

#sidebar-box {
    max-width: none !important;
  • Thank you for the updated note. I mentioned you on a comment with the original answer and +1 your comment. Dec 7, 2022 at 7:10
  • TY, and noted min-width also works the same; " min-width: 20px !important; "
    – u2n
    Apr 8, 2023 at 0:58

reload the browser

  • How is this better than accepted answer?
    – Toto
    Jul 2, 2022 at 15:49
  • there have been changes in how to locate the profile folder for some firefox versions Jul 27, 2022 at 22:52

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .