Sinbad said:
Reset the Internet security zone to its default setting, make sure to
close all instances of IE (check the Processes tab in Task Manager to
make sure there are no instances of iexplore.exe), reload IE, and test
again.
Use BHO Demon to see what BHOs (browser helper objects) you have
installed that will modify IE's behavior or add functionality. Spybot
S&D also has a BHO utility to list them but BHO Demon is better, plus
they maintain a database to provided info on the known BHOs.
If Firefox is working then the problem never was with a Layered Service
Provider (LSP) chained into your TCP layer. If it was broken, Firefox
wouldn't work, either.
Did you yet purge IE's temp file cache, including offline content? Have
you tried purging your cookies.