Google have done for Firefox for me - the Google toolbar is not being updated (it only worked in v5/6 with the compatibility add-on) and now it is impossible to sign in.
Ironically Chrome doen't have the same features (at least not all together in the same easy to use toolbar) so I've gone back to Internet Explorer

.
There seems to be some twisted logic somewhere when Google take away a feature in Firefox that they don't (or not obviously) provide in Chrome but are happily continuing to support in IE.
"If I have not seen as far as others, it is because giants were standing on my shoulders."