OPIE is a Firefox add-on that lets you backup your other Firefox add-ons. While that might sound a lot like FEBE, another popular Firefox extension, there's at least one major difference: OPIE works with Firefox 3. Actually, make that two major differences, because OPIE also gives you the option of saving multiple extensions in one file, while FEBE users will need to install a separate application called CLEO.

You can use OPIE to choose from your list of installed plugins, selecting just the ones you want to backup, and where you want to save them. The result is a file which you can use to load your favorite plugins into Firefox on another machine.

[via GHacks]