Top 5 Firefox2 extensions for educators

I’m in the process of making a bunch of Screencasts for educators on using Firefox2 and thought I’d ask anyone who is interested to chime in.

What are the top 5 Firefox2 extensions every educator should have?

Such a simple question I know.

My debate right now is whether to promote zotero or diigo. I’ve just stated playing with diigo and have been using zotero for awhile. One big difference I think is that to use diigo you need to create a user account on their site. Now that’s not bad if you’re a geek like me and you have accounts all over the Internet. But if you’re a teacher…you know the type, the type that say “Another account? How am I going to remember all these username/passwords?” is Diigo worth it? Or is a simple extension like zotero better with no online account needed? Or is there something better that I’m missing.

My list so far Bookmarks Great for personal and classroom use
Zotero research tool A great research tool for all ages!
Googlepedia Shows you a relevant Wikipedia article aling with your google search results.

So, what are your top Firefox2 extensions?