Unlock the Sidebar Width in Firefox

This post will guide you through unlocking the sidebar width in Firefox. It will let you resize it beyond what is possible by default. We will be setting both the maximum, and the minimum width. You will have a chance to customize these values once at the right step.

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.

Overview

1. Open about:support.
2. Locate your Profile Folder.
3. Open your Profile Folder.
4. Create a new folder called chrome.
5. Inside the chrome folder, create a new file called userChrome.css (includes the file extension).
6. Copy and paste this in it: #sidebar-box { max-width: 40% !important; min-width: 300px !important; }.
7. Customize the width to your preference.
8. Open about:config.
9. Find toolkit.legacyUserProfileCustomizations.stylesheets and change its value to true.
10. Restart Firefox.

Step-by-Step Instructions

1. Open about:support

In a new tab, navigate to about:support.

2. Locate the Profile Folder

Under Application Basics, find Profile Folder.

3. Open Profile Folder

Locate and click the Open Folder button next to it. You’ll find it next to an address similar to:¹

%appdata%\Mozilla\Firefox\Profiles\your-profile-id.default

Note: In Windows, %appdata% is equivalent to:
C:\Users\your-username\AppData\Roaming.

4. Create New Folder chrome

Inside your Firefox Profile Folder, create a new folder named chrome.

5. Create userChrome.css

Inside the newly created chrome folder, create a new file named userChrome.css.

6. Copy and Paste Its Contents

Copy the following code, and paste as content inside useChrome.css and save:

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

7. Customize the Width

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

8. Open about:config

In a new tab, navigate to about:config, and search for:

toolkit.legacyUserProfileCustomizations.stylesheets

9. Change the Value

Change its value to true.

10. Restart Firefox

Finally, restart Firefox for the changes to take effect.