A variant of the Vundo trojan is known to cause Firefox to have problems loading certain websites. Symptoms of this infection include:
Problems loading certain high-traffic sites, including Google, Yahoo, MySpace, Facebook, and more.
The affected pages never load - the Firefox activity indicator may spin for several minutes, or the status bar may show "Done" on a blank page.
If you're having a problem loading sites other than the one described above, see the Error loading websites article to see if it addresses your problem. You can also check your Internet security software - resetting permissions for Firefox can often fix similar problems.
There can be other causes of the symptoms described above. Before attempting these instructions, try the methods described in the Troubleshoot and diagnose Firefox problems article to see if they will address your problem.
Search for malware
Not all variants of the Vundo trojan can be detected or removed by malware scanners. However, you should scan your computer for infections first: