If you use many search plugins for Firefox, you might be interested in a better way to organize them, rather than just choosing from a giant drop-down menu when you want to switch the search engine.
The Organize Search Engines extension for Firefox will let you re-organize all the search engines into folders, which can be very useful for separating out the commonly used ones from the specialty searches.
After installation, you can go to "Manage Search Engines" to make your changes:
You'll now see options to create folders and separators, just like in the manage bookmarks dialog. The one important thing to note here: You must use the OK button to close the dialog, or else your changes don't seem to save.
Once you've organized into folders, you can change between them using the regular drop-down menu:
This extension is especially useful, however, if you also install the Context Search extension, which will let you right-click on a selection in the page and choose from the folders of search engines:
The one feature that didn't work for me was the "Edit Keyword" option... I assume that part is incompatible with some other extension I'm running.
Download Organize Search Engines from Mozilla Add-ons (discontinued)