I had a problem with a 2820Vn after a failed firmware update, did hardware reset. When I tried to downgrade the firmware from the suspect 3.3.7.2 to 3.3.5.2 something went wrong. No problem - reset and start again. This is a Windows 7/64 system.

I found problems with the password. The firmware upgrade utility in router tools would start with the right password, but always failed with a timeout (despite making sure everything was on a fast drive, and changing the default timeout from 5 to 55 seconds). The router was connected properly, no question about that.

The web browser wouldn't log in with any password : name admin/pw admin) (default after reset), blank, or old password. Together with the updater program problem, I couldn't install firmware or access the router. Telnet worked OK and could change password, but web browser failed again, not recognising the password just set, and accepted, by Telnet. In most cases used name "admin" or blank.

The browser interface immediately worked, first time, after I moved from Firefox latest (13.0.1) to IE latest (updated 14 July 12). I did a .rst firmware downgrade to 3.3.5.2. The inference, which I've not tested further (and the reason I'm posting this), is that Firefox has some login issues when used after reset for Draytek web interface (I've had problems before), though it mostly works with the interface. Loading the previous configuration I was back in business.

In the event of router problems in future I will leave the router off for a while (just in case, probably not relevant) and reset it, then use IE. Firefox is fine for routine management. Always make sure to back up configuration after every change.