Firefox: There are a lot of great little configuration tweaks one can pull off by editing Firefox's about:config settings, but only if one knows what those sometimes cryptically-named settings do. The Prefsearch extension automates Google searches for each setting.
That may not sound like much of a help, compared to linking each entry to, say, the MozillaZine Knowledge Base, but a Google search for an about:config setting often reveals some pretty helpful, plain-English explanation of what the setting really does in common use, and what people have thought of the change after it's switched. That's because those searches often pull up form posts, help sites, and, er, Firefox-obsessed blogs with some helpful breakdowns of the nitty-gritty of each setting.
If you're frequently looking for the no-extension-needed fix for your Firefox needs, Prefsearch might be one extension worth installing. Free to download, works wherever Firefox does.
Prefsearch [Firefox Add-Ons]