4.11 doesn't seem to be a valid file for the TA900 Gen 2. Those releases are of the form T900G2A-R1n-n-n-E.biz . Unless you need some extremely recent feature, I'd go with T900G2A-R11-10-6-E.biz as it is extended maintenance and will be supported through the end of next year. Older firmware isn't supported which can make for a frustrating experience when you need help from Adtran. Even if it isn't a firmware issue they'll tell you to upgrade to a newer version before they will help you.
Make sure there's room on the flash for it and that the file is valid for that platform. The browser closing could be a bug in the browser or computer. Try a different browser or use tftp.
Also read the release notes. If it's a very early unit you may need to update the bootflash before it will run recent firmware.
