Rated 3 out of 5 stars

Looks good, but two (minor) features missing -

Can the list include options for "Firefox" user agents (eg different version?)

Can the add-on allow "customise the list" option (so you can enter multiple custom agents for choosing; right now you must enter each time "new")

This would be very good.

This review is for a previous version of the add-on (0.3.2). 

I try to add only the main User-Agents to keep it simple, as you can see only Internet Explorer has different versions.
I could even add a long list of User-Agents, but it really would be used?
(Ohh! You reminded me to add Firefox Mobile in the list :D)

A "customize the list" is a really good idea and I think it would help anyone in need of other User-Agents (as in his earlier suggestion). I will arrange something for next update.

Thanks for the review!