The browser you use doesn’t play any part in the actual update process.

Try a repair of avast.
XP - Add Remove programs, select ‘avast! Anti-Virus,’ click the Change/Remove button and scroll down to Repair, click next and follow.

Vista, win7 - Repair of avast. Control Panel, Programs & Features, uninstall a program, select ‘avast! Anti-Virus,’ click the Change/Remove button and scroll down to Repair, click next and follow.

You may need to reboot after the repair. This has in the past resolved this out of sync issue between reported and actual VPS version.