If you’re looking to install Google Gears on OS X, installation order can be somewhat important. The Safari version installs as a standard OS X browser plugin and will be picked up by all the browsers on your system. Sounds good, except that the Firefox version is actually a standard Firefox XPI extension and the two will conflict — you actually won’t be able to install the XPI unless you first disable the plugin via the Tools > Add-ons > Plugins menu option.