Remove/hide fingerprintable UI options
Firefox has a lot of options that allow websites to fingerprint users who set them. Obvious ones include the Font and Color preferences, the Do Not Track header option, and maybe even the cookie and cache preferences. There's probably a few more, too.
Not sure the right way to do this, either. I think hiding the UI but leaving the about:config options is the best move. That way, we protect users who don't know any better, but still allow users who are obviously totally smarter than us to set prefs without constantly listening to their nerdrage. (Of course, we'll probably hear their nerdrage anyway until we have a well-circulated FAQ entry...)