Why Would Anyone Want to Do This?

• To enhance the use of the Firefox Side View extension.
• To compliment the use of one of my Firefox sidebar extensions.

Step-by-Step Instructions

1) In a new tab, navigate to about:support.
2) Under Application Basics, find Profile Folder.
3) Locate and click the Open Folder button next to it. It will be next to an address similar to: %appdata%\Mozilla\Firefox\Profiles\{profile-id}.default ¹
4) Inside your Firefox Profile Folder, create a new folder named: chrome.
5) Inside the newly created chrome folder, create a new file named: userChrome.css.
6) Copy the following code ², paste as content and save: ³

#sidebar-box {
  max-width: 40% !important;
  min-width: 300px !important;
}

7) Finally, in a new tab, navigate to about:config, search for toolkit.legacyUserProfileCustomizations.stylesheets, and change its value to true.
8) Restart Firefox and test it out!

1. %appdata% is equivalent to C:\Users\{username}\AppData\Roaming ↩

2. After Firefox 107, #sidebar was deprecated, and #sidebar-box was introduced. ↩

3. You may change the units to any length you find more convenient. ↩