I used to middle click on the back button in firefox to open the last page in a new tab.
Unfortunately this stopped working for me on Ubuntu 14.04 x64.
I tried to remove it via
sudo apt-get purge firefox and reinstalled it, but nothing changed.
This is at my home computer. At the office I run the same Ubuntu version but x32 where this feature still works and I don't know why. It just stopped working from one moment to another and I don't remember what I could have done... I also tried other mice...
It really annoys me, because I got used to this workflow. Is there any chance this is a bug or something else you know?