I don't have Firefox 27 around, but I tried Firefox 28 with latest URL Fixer from AMO (4.1), added a custom correction from google.com to archive.org, and it's working correctly: if I type a google.com URL in the address bar, the domain is changed to archive.org.
Does URL Fixer work for you in a new, clean profile?
If so, your best bet is probably to try Standard diagnostic
on your main profile.
Please post your findings.