I have realised that the two "edit" links on my Preferences page (to edit favourite and ignored tags) can't be clicked either. Checking the Web Developer>Network activity, I can see the following messages:
The popup you get when cliking on the stackexchange icon or when hovering on your user name have stopped working a few weeks ago on some pages.
For example, it works on these pages:
But it does not work on those pages:
I'm using Firefox 23 on Windows 7 (just upgraded to Firefox 23.0.1 but same behaviour). The behaviour started a few weeks ago, on 3 different PCs.
The popups I'm talking about: