I've just tried to install Google Gears and been told that neither Firefox 3.5.1 nor Safari 4.0.2 are supported.
The browser support page lists both browsers as options but on the basis of "or later" (so Firefox 1.5 +) so I assume that these versions are too new.
Anyone with any experience of using Gears know how quickly they support new versions? There doesn't seem much point in installing it if everything I upgrade my browser (generally as soon as possible) it breaks Gears.