My wife's laptop had a serious problem right after upgrading to Firefox 10. I don't think it's related as Firefox is an application and the problem itself is hardware-related, which is the broken ethernet.
She told me that after upgrading to Firefox 10, the ethernet icon on her laptop was missing and i checked using ipconfig and it's really gone. I restarted the laptop with some hope that it might just a glitch, but unfortunately it's not. It happened some time ago, and i hope by restarting, all will be fixed, but i was wrong. It's really gone and since it's wireless chipset is also having some problems, the laptop is connectionless for now.
I will bring it to the computer store to be repaired by tomorrow and hopefully it can be fixed, since ethernet port in a laptop is not the same as in PC/desktop in which you can just simply replace the card by another one. For now, i will just ask her to simply backup all her data just in case we had to reinstall the Windows again (it hasn't been reinstalled since 2008 since there was no problem with the system).