Do you use the Remote Desktop function in the Professional editions of Windows?
If you do, you might have noticed that, after the nth Firefox update, you can't open it anymore.
What to do?
The problem is that Firefox 13 (or 14, if you read this article tomorrow, or 18, if you read this article next month) wants to use the hardware acceleration of the video card, but they forgot that, in remote desktop mode, the video card is virtual, hance without hardware acceleration, making Firefox freeze at startup... 
We will solve the problem in two easy steps:
Start Firefox in safe mode
Some time ago, in the start menu there was an icon "Firefox (safe mode)", then they had the great idea to make it much more intuitive. To start it in safe mode you have to press SHIFT (on Windows) or OPTION (on Mac), (on Linux instead they opted for a command line switch, because it's cooler).
It's SO OBVIOUS that pressing SHIFT will start it in safe mode, how I couldn't think it before??? 
Don't check any checkbox, otherwise you will reset all the settings!! Just press continue!
Ps: if you get a message that Firefox it's already running, close it from the task manager.
Disable the hardware acceleration in Firefox
Now, Firefox will startm go to Options=>Advanced Tab=>General Tab=>Use hardware acceleration
Done! Firefox will work again! 