Works fine with SeaMonkey 2.39 Rated 4 out of 5 stars

I only did some short tests with SeaMonkey German 2.39 final Mozilla/5.0 (Windows NT 6.1; WOW64; rv:42.0 from official download area) Gecko/20100101 Firefox/42.0 Build 20151103191810 (Classic Theme) on German WIN7 64bit for "Bug 1242294 - Advertise exactly Firefox when compatMode.firefox is true" <https://bugzilla.mozilla.org/show_bug.cgi?id=1242294>:
Core function works fine.
List of available user agents is difficult to find.
May be shipped user agents need an update? I can't imagine for what IE6 might be useful.

appears to work well with PM Rated 4 out of 5 stars

How can I get it to SAVE the default user agent each time i start up Palemoon as it seems to keep setting it back to default ?

Rated 5 out of 5 stars

Having a website tell me that my browser out of date is annoying, I had to use this to get around that. Website developers: make a website that's lightweight and runs on anything, I shouldn't have to update my browser every 6 months just to click "add to cart" or read a news article.

I use this to watch HD videos Rated 4 out of 5 stars

Probably not the normal case usage though. But this lets you get around dumb filtering decisions. One star off as you have to hunt around for agent profiles that aren't included, but those aren't terribly hard to find.

However this combined with FFMpeg, lets you watch HTML5 HD via WebM while still eking out life on a machine with WinXP as the OS. (Don't ask how I figured that out.) Apparently some content or content quality is blocked if those sites don't think you'll meet their ideal requirements, and this add-on allows for a workaround.

Works with a caveat Rated 5 out of 5 stars

Works beautifully with a caveat. You also have to install user_agent_js_fixer to get to work on most web sites now-a-days.

Additional User Agents are found here: http://techpatterns.com/forums/about304.html

Request for Enhancement: allow certain web sites to be fixed to a particular user agent. (UA Control does not work with user_agent_js_fixer.)

change UA automatically by site Rated 4 out of 5 stars

Nice addon :)
Perhaps it could change the the UA specifically when loading certain urls?
Or one could change the UA for a certain tab?

This would be very nice :)

Rated 5 out of 5 stars

Works flawlessly. Icon can be placed anywhere from menu > customize.

Does not work. Rated 1 out of 5 stars

Makes no change to user agent string regardless of which profile you select.

NOT WORKING HERE. Rated 1 out of 5 stars

Does nothing on this site.www.whatsmyua.com/

Rated 1 out of 5 stars

Did not add button. No way to activate websites. If it takes more than five minutes to figure out how to turn it on, something is wrong.

Rated 5 out of 5 stars

The best user agent switcher out there. I use both the firefox and chrome versions of this addon.

Pointless, only works briefly. Rated 1 out of 5 stars

The author knows the user agent resets every time Firefox is started but does nothing to deal with this.

Çok kullanışlı Rated 5 out of 5 stars

Çok kullanışlı. Ben kullanıyorum tavsiye ederim.

Still working Rated 5 out of 5 stars

For linux users this works great, no issues at all.

A list, if you don't know how to find one.
http://techpatterns.com/forums/about304.html

This user has a previous review of this add-on.

Rated 1 out of 5 stars

Right now, has been disabled for a week over numerous restarts ... but still exists in my menu bar and still starts up each time firefox does.

VERY disconcerting

Reset on startup Rated 4 out of 5 stars

This is a great addon. To be perfect I had to edit the extension to get rid of that annoying reset on close, to keep user agent between sessions. Fortunately it worked! :D

Rated 3 out of 5 stars

Very few pre-defined profiles. You have to pay for yourself, which is inconvenient. Crooked is integrated in a new menu, ugly.

It's perfect Rated 5 out of 5 stars

It works as mentioned. Great addon.

It really works on latest Seamonkey 2.33 Rated 5 out of 5 stars

Althought it is stated that this add-on doesn't works on SeaMonkey 2.33, it is working.

Also, it is better to download the new updated user-agent strings throught the link provided on the Options dialog box.

Rated 5 out of 5 stars

This add-on is working well for me emulating a mobile device on my desktop to benchmark search engine results in preparation for Mobilegeddon on 21st April.