As a student, or someone learning it's pretty important to be able to annotate PDF documents or websites. Recently, I had to go through extensions but yeah... Basically I think it would be handy to annotate websites/PDFs in Firefox and have a side pane which shows all your saved annotations. For organization, perhaps some folder-type structure. Right now I ended up using Lightshot.

I couldn't find any suitable addons that were quick, easy, saved automatically, or didn't bug out or was for free. This just sound suitable to be a Mozilla Test Pilot project...