The about:addons page is an HTML page and this code needs to be in userContent.css to hide the notice.

You can add this code to the userContent.css file.

• http://kb.mozillazine.org/userContent.css

@-moz-document url-prefix(about:addons){
 #private-browsing-notice { display:none !important }
}

The message is still present on this one as well after applying that code as well.

You did place the code in userContent.css and not in userChrome.css ? I think that Firefox 67 still needs userContent.css, but you can try to add the code in userChrome.css as well. Try to code in userChrome.css without or above the default @namespace line.

cor-el said

You did place the code in userContent.css and not in userChrome.css ? I think that Firefox 67 still needs userContent.css, but you can try to add the code in userChrome.css as well. Try to code in userChrome.css without or above the default @namespace line.

Removing the top part took care of it.

Thanks again sir.

If there is any data appended on the location bar after about:addons then you have to use url-prefix() instead of url() if that line is what you are referring to. This is probably better anyway. This line specifies where this code should be applied.

• https://developer.mozilla.org/en-US/docs/Web/CSS/@document