I can't open my Firefox. I don't remember well how this problem came on, but apparently I've never made any changes to my computer or Firefox itself since the last time I could launch it successfully. I'm using Windows 7 Pro 64 Bits. Now, whenever I open Firefox, there is always an error message saying, "Couldn't load XPCOM". I haven't reinstalled Firefox since I don't wanna lose my important bookmarks. I hope you can help me resolve this problem.
This message indicates failure to load
xpcom.dll. Check the installation directory (most probably
C:\Program Files (x86)\Mozilla Firefox\) if it is there.
I got this error after firefox notified me to upgrade and I clicked to do so. I used chrome browser to download the newest version of firefox (22) and it works OK now (all my settings retained). xpcom.dll is not now in the mozilla firefox directory. Maybe it is not used in the latest version.
Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
You can re-install Firefox by just making a backup of your settings first. Do it via cloud sync (go to settings and click on sync) or backup the folder in your user directory.
Otherwise here is a thread on mozilla.