Mozilla Foundation released lately security update 184.108.40.206 for FireFox which broke my favorite Twitter client TwitterFox by that links in posts did not open anymore. I did a quick dive into the source and after a few tries I had a basic fix running. It is available for download here.
To install close FF, locate your profile directory and copy TwitterFox.jar to [profiledir]\extensions\firstname.lastname@example.org\chrome\
The fix will remove the ability for TwitterFox to locate a tab, that has the URL already opened but I can easily live without that.
The author is informed and we will hopefully see an official update shortly.