Hello and thanks for your feedback,
You are right, I'm sorry if you are experiencing issues with iFamebook (what's happening is that Facebook code changed recently, so the extension is not working anymore). We are working on a bug fix to release as soon as possible.
About the Firefox freezing issue, I think that iFamebook has nothing to do with that (besides, iFamebook doesn't show any "options" button under the Add-ons menu). However it has the "remove" and "disable" buttons, that you can use to uninstall the extension from your browser.