Something that really annoys me about Google Groups is that it wastes tons of horizontal space. As a result, you can't read 80 column wide messages without wrapping, unless you have a full screen browser. I don't use a full screen browser.

With Firefox 1.5 and Mozilla 1.8, there's a feature that allows custom CSS rules for specific domains, specific URLs, or specific URL prefixes. You can also do this with older versions of Firefox and Mozilla with the UriId extension. It's like Greasemonkey, but for CSS instead of Javascript. In userContent.css, you can add rules of these forms:

@-moz-document domain(, domain( { ... }
@-moz-document url( { ... }
@-moz-document url-prefix( { ... }

Using this feature, I “fixed” the thing that annoyed me about Google Groups.

@-moz-document domain(, domain( {
  #rn {
    display: inline ! important;