The problem doesn't resolve, I then re-install 17.0.1 and works fine. Have tried this install with 18.0 and 18.0.1 same results
Do a clean reinstall and delete the Firefox program folder before reinstalling a fresh copy of Firefox.
Download a fresh Firefox copy and save the file to the desktop.
Uninstall your current Firefox version, if possible, to cleanup the Windows registry and settings in security software.
Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.
Your bookmarks and other profile data are stored in the Firefox Profile Folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.
I followed the steps you have suggested, when I started FF 18.0.1 I still received the error "Could not load XPCOM". I reran this process to delete and remove FF 18, then ran Malwarebytes, no problems found, and cleaned the registry, then reinstalled FF 18. again the error "Could not load XPCOM" appeared again. I have reverted back to FF 17. Any other ideas to resolve this?
You did delete the Firefox program folder, because such issues are usually caused by a failed update to some files?
Yes I deleted the Firefox program directory as per instructions. I think I will try a custom install and select a different directory for the program installed location.
I just installed Firefox 18.0.1 in a different directory and Firefox now starts error free. Thanks for your support cor-el your input lead me to the solution,