Please go to www.getfirefox.com and download and install Firefox 18.0.1 from there.

Solved. Thank-you.

My problem was exactly the same although my version of Firefox was up to 19.1 by now. I followed instructions downloaded again, I hope it gets fixed but it's far to early to say for sure just yet. What do I do if I think I have two or more versions installed at the same time somehow? Is there a safe recommended free software Uninstaller that will get rid of absolutely every bit of a download in every nook and cranny of my device, and a recommended way of starting again?