Hi Jack,
We had several support cases submitted by our customers where they reported the same problem. In all cases, the cause of the problem was incorrect applying of the patch. So, please check whether you copied all the files to the correct locations.
If this does not help, here is a couple of things you can try:
1. If you are running Win7, Vista or Win2008, try running TestComplete with elevated rights (use the "Run as administrator" context menu command on the Desktop) - this may be required if Firefox is started with elevated rights.
2. Try running Firefox in safe mode and check the "Disable all add-ons" option in the dialog that comes up: http://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode?redirectlocale=en-US&redirectslug=Safe+Mode
When Firefox is running without add-ons, check if you can test the page with TestComplete.