great add-on Rated 5 out of 5 stars
Awesome. It still translates entire page in-place better than almost any other translation add-on. It doesn't redirect you to the google translate site where your page would be framed and may lose functionality.
It even automatically translates new text that appears dynamically on the page (ajax etc.). And you can hover to get original text where you can see alternative translations of the pieces, just like in Google Chrome or in the translate-some-text feature on google translate site.
S3 Google Translate add-on is similar but has more features (such as automatic translation of sites you've visited before, and text snippet translation features) and has been updated more recently. Still, they both deserve 5 stars.
There's a bookmarklet that does something similar to this add-on (from http://googlesystem.blogspot.com/2009/11/google-translation-bar.html ).
All appear to be based on the old google toolbar translate feature and invoke similar code from the google translate api site. All of these use the unsupported google translate public api, so they may stop working at some point, but in the meantime they're great.
Unfortunately, translation by this extension is blocked by Flashblock.
I would love to see an option to invoke this automatically on *every* site, but when it's detected as already being in the target language then do nothing.
BTW to nirvin, go into the add-on's options to enable toolbar icon, add-on bar icon, and/or context menu option. For toolbar icon you might have to right-click-->Customize and drag it from the tool palette to a toolbar.