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?

  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 {
  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 '19 at 19:16
  • Did not work on FF 70.0.1. – wha7ever Nov 12 '19 at 15:46
  • 5
    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 '19 at 8:42
  • Does not seem to work on FF 71. – Marcin Orlowski Dec 18 '19 at 12:28
  • 1
    How do you guys know all of this stuff wth? – 55 Cancri Jun 28 '20 at 13:49

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