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In Mozilla Firefox, I want to create userContent.css which overrides the CSS of a site, say this one.

Where should I create the file? Could you please describe it based on Windows 7?

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2 Answers 2

up vote 27 down vote accepted

Step 1 : Open Firefox, Go to 'Firefox' menu at the top-left of the browser.

Firefox --> Help --> Troubleshooting Information --> Open Containing Folder

Step 2 : Create a folder named chrome

Step 3 : Create a css file userContent.css

Step 4 : Copy the following code to the files userContent.css

Step 5 :

@-moz-document domain(your_domain.com) {
opacity: 0.05 !important;

Step 6 : Replace your_domain.com with specified domain name, say superuser.com if we need to format the images in superuser.com

Step 7 : Resatrt user browser

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A small update / modification for step 1; the Troubleshooting Information opens up a link about:support and in my Firefox (v20 nightly build on Ubuntu) it has an entry named "Profile directory" with a button "Open Directory" which opens up the profile directory /home/tripleee/.mozilla/firefox/asdf1234.default/ in Nautilus. –  tripleee Jan 3 '13 at 10:38
You can remove @-moz-document domain("...") to apply the style to every pages. –  Nicolas May 30 '13 at 8:26
Why is it supposed to be in the chrome folder? –  Septagram Dec 18 '13 at 8:01
@Septagram I think it's just always been that way… as I remember, chrome could also contain userChrome.css, which would style the browser interface ("chrome"). –  sam Sep 27 '14 at 18:05
I know the OP asked about Windows 7, but for OS X users the path is ~/Library/Application Support/Firefox/Profiles/<profileid>.default/chrome/ –  rlovtang Dec 1 '14 at 15:54

The add-on ChromEdit Plus will do all this for you.

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