I see that you have Firefox 6 installed. You're way overdue for an upgrade. If you installed Firefox 31 from the official site, you shouldn't have any problems. Mozilla downloads are clean *mozilla.org/firefox

If you got Firefox from mozilla.org whether stub or full setup from https://www.mozilla.org/en-US/firefox/all/ then there should be no form of viruses, trojans, malware, ads or such. No version of Firefox for Windows, Mac OSX or Linux has with the exception of a certain locale contrib build like eleven years ago as it was not until Firefox got to version 1.0 that there were other official language builds besides en-US then. Some antivirus applications give false positives with Firefox related stuff especially depending on timing of Firefox release and new definitions update, especially with the stub installer. There was a post a couple days ago about McAfee giving a false positive with the stub installer of Firefox 31.0. If it was true that Firefox 31.0 for Windows came with a virus it would very likely be a active topic here and on tech sites. Firefox Setup 31.0.exe en-US Detection ratio: 0 / 50 [https://www.virustotal.com/en/file/f502ce4aa6e8f983df3fc787f4d6d473b7bc5551861f382cc67c802683903803/analysis/1406406611/ virustotal results link] Firefox Setup Stub 31.0.exe en-US Detection ratio: 0 / 53 [https://www.virustotal.com/en/file/048f47c2d87b7134cb6a2eba1ae962ef7c7dc77cea4512fcb9e86ab738df48ba/analysis/1406406743/ virustotal results link]

It was just a mistake in antivirus program/