Will the developers of all the AdBlock variants need to worry about their accounts being blocked as well (as they surely are against Facebook's terms of service as well)?
If you meant to assert that they shouldn't be allowed to: why not? It's their website, and their TOS that's being ignored. They have every right to.
So why is it one rule for this guy and another rule for AdBlock (or any other extension)?
I run AdBlock, and was shocked to see the amount of adverts on "normal" computers, truly shocking. Does that mean you should ban my account? They have a Facebook page: https://www.facebook.com/adblockplus
Maybe Google should stop offering AdBlock as a Chrome extension, given that advertising is a huge chunk of their business?
You are able to achieve a similar Greasemonkey Firefox plugin. You just need to find the correct scripts... https://addons.mozilla.org/en-US/firefox/addon/greasemonkey/
The guy should just open source it, let's see Facebook try and keep up with that one.