Vendor/Version browser detection strikes again!
When attempting to view the new Yahoo! home page in the development version of of Firefox 2 (also known as Bon Echo), I was presented with the following lovely page:
If Yahoo! had made the requirement to be any Gecko-based browser based on branch 1.8 or later (which includes Firefox 1.5), then I would have been able to see their new design without having to fudge my user agent.
If you must restrict access to specific Gecko versions, use something like getGeckoRv() which can be used to detect the version of a Gecko-based browser independently of its branding or vendor/version.