Puntuado con 2 de 5 estrellas
At first sight it seems really good - lots of browsers &amp;amp; browser versions, even different OSes. But as others said, it is REALLY outdated. We are at FF 15 now, and the highest UA available is FF 4 ???!!
The real problem is that it totally ruins your ability to download/install almost any extension, no matter what UA you choose. This is part of Mozilla's fault, for making their website oh-so-helpful and denying you from downloading an extension unless your browser is a version of FF compatible with the extension... So now, all extensions I see are grayed out no matter what, and the download button is a dead image with no interaction. Srlsly, wtf. Why would Mozilla not let me download an XPI for FF15 while using e.g. IE6, or Opera9 ??
Anyhow, it's also a lack of thinking from the designer of this extension, since you simply cannot revert to the original UA prior to installation, not even after you kill the extension.
Not to mention you should be able to enter your own (save-able!) string(s)...
I'm only giving 2 stars for the effort.
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I MADE AN UPDATED VERSION OF THIS EXTENSION, HERE: