In my district, I'm starting to prepare a "universal design" version of Firefox. To this end, I've been on the hunt for great add-ons. I was recently reading Richard Byrne's blog and I saw a Simple Timer add-on. It could help students manage their tasks and their efforts when working on online research.
My ultimate goal is to have the "universal design" version of Firefox that I compile loaded onto every computer over the summer. I will couple this with professional development to help teachers encourage students to utilize universal design features appropriately.
Do you have any Firefox add-ons that you can't live without? Let me know.