it isn’t my favorite, but i recently downloaded (and am really enjoying) Firenes It has over 2500 Nintendo games that you can play on your browser. And I remember playing many of these as a kid so it makes me reminiscent. Just get the addon, and choose from the ridiculously big variety of games to open in a new window and you can play with fluthering :)
Other addons I like: Stumble and Sxipper (for form filling and remembering username/passwords). OOooh and I also use Google Translate which can translate any page and/or sentence into English or whatever language I want really. That’s a useful one for sites in different languages of course.
All of these are compatible with FF3