Google has clearly abandoned Gears; they no longer support it (about a year ago!).
They switched to focus on HTML5 and other related new browser features. Essentially, they say that all the functions provided by Gears can be done using HTML5.
Here's a link to an article saying they drop it (but there are many others if you use Google for it):
http://latimesblogs.latimes.com/technology/2009/11/google-gears.html
The downside is that not all browsers support all the HTML5 features that are needed to replicate the Gears features, therefore, condemning this, they have disabled support for some browsers. Chrome is fine, of course! But other browsers are catching up - of course, Firefox 4 should be fine.
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