Of course, the best way to clean up your context menu is to make sure that you don’t have any add-ons that you barely use. Even without a ton of add-ons, though, Firefox’s context menu can still seem like a lengthy medieval scroll. FfChrome will help clean it up without depriving you of those options when you need them.
When you install it, your context menu will only show the essential menu items. By hovering over “Show All”, you can see everything else, so it’s only there when you need it. And, if there’s an option you want to always show up on the basic version of the context menu, you can configure that in the preferences.
FfChrome is a free download, works wherever Firefox does.
FfChrome [Firefox Add-Ons via GHacks]