All of a sudden my tab key quit working in firefox as well as copy and paste using ctrl+c, v, etc.
It took me a long time to realize it was only an issue in Firefox too… I was about to buy a new keyboard!
Luckily I remembered updating some plugins for firefox recently, so I disabled a few plugins and it fixed the problem. Now i can tab! yay!
To manage your addons go to tools > manage add ons > select an add on and click disable > then click restart firefox > press tab a whole bunch to test… repeat as many times as needed to get tab working again.