I just went to YouTube in Iceweasel and got an annoying "Your version of Flash is vulnerable" (I have the latest Linux Flash). When I clicked on the download link, it wanted to download Firefox.
In Iceweasel, go to Tools-->Add Ons, and search for "Browser User Agent." There are a number add-ons that will allow you to spoof your user agent string.
I've never used any of them, because I mostly use Opera, but one of them should do what you want. I know that I have a user agent extension for Opera so I can display the proper user agent string in LQ (that's why user agent reports "Debian" on this computer) and it works like a charm.
If your Vista is borked, why not just install a Linux and say good-bye to Windows? If the box ran Vista, it should be plenty brawny to run any contemporary Linux.
I'd recommend Mint. It works very nicely and intentionally arranges its interface to be an easy transistion, though, as you observed in another thread, it is still different underneath.
Last edited by frankbell; 02-10-2014 at 07:38 PM.