After some research, this is what I found:
1) Extracted from here:
"I had the same problem and found a solution. Hopefully this may help some of you if your situation resembles mine.
My problem was that my firefox browser opened to a blank page, and the navigation buttons were grayed out, and not working.
I tried many things, thinking that it may be related to my norton internet security, or with firefox itself. I even uninstalled and reinstalled firefox only to get the same problem. I also tried to restore my computer to an earlier time, and even this did not work.
Then I realized that I had added a new connection to the internet a few days ago, so that I would be able to use my cell phone as a modem for internet access---This was done only to see if it was possible, and it is. Anyway, it was the settings in this connection that interfered with my firefox browser.
So if you have a situation similar to mine, you may want to go back and check the modem settings you may have for internet access, and undo these changes, or delete the new dial-up connection if you may have created one before these problems arised. Hope this helps, good luck."
2) Extracted from here:
"My firefox is now working great. What I did was opened as follows. 1- I opened norton 360. 2-Click on manage firewall. 3-Click on the tab program rules. 4- Scroll to mozilla firefox and click allow (mine read custom). 5- Exit out of norton, and reboot computer for it will not work for you until you reboot. 6- Start firefox, and it should work."
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Sorry if this isn't the solution, but meanwhile I think you can use an older version ;)