Facebook – Why Can’t Paste into Comments in Firefox?

For more than 3 months Ctrl+V doesn't work when I want to paste something into Facebook comments. I can only drag and drop into the comment box. But my friends say they don't have problems with it…

Upon Ctrl+V the UI screws up and the caret doesn't insert characters where it blinks, also home and end and other navigation buttons begin to scroll the page instead the caret in that edit box. Only way to get out of there is refreshing the whole page. Looks like the whole edit control is controlled and implemented in JS.

If I create a new firefox profile, it works. So I'm suspicious that some addon causes the problem. But I don't want to lose my entire profile by starting a new one just for the sake of Facebook's stupid tricks.

So what I tried so far:

• Delete all cookies and the entire browser history: no avail.
• Erased the browser cache: no avail.
• Disabled all addons (although I uninstalled none): no avail.

What else can be screwed up? Maybe disabled addons still have an effect on the browser?

I'd like understand what happens and fix the problem based on that instead of the usual "try format your hdd and reinstall you OS" tips, other forums often give.