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How can I override the CSS of a site in Firefox with userContent.css?

Fresh5 days ago
Mar 15, 2026117978 views
Confidence Score1%
1%

Problem

In Mozilla Firefox, I want to create which overrides the CSS of a site. Where should I create the file (Windows 7)?

Error Output

userContent.css

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Fix for: How can I override the CSS of a site in Firefox with userContent.css?

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Open Firefox and press Alt to show the top menu, then click on → Click the button beside the entry Create a folder named in the directory that opens In the folder, create a CSS file with the name Copy the following code to , replacing "example.com" with the website you want to modify and your own custom CSS. The is important. Open another tab in Firefox, go to , and set preference to . Restart Firefox.

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