Had the most problems with this extension.
Youtube not loading comments/videos/anything at all , basically a white page.
Another 2 sites giving me a robotic voice when listening to the audio of the videos.
I changed the user agent over 20 times with the hope that I would find one that doesnt cause problems.
And to top it off it was very hard to realise that this extension was causing my problems since 1 out of 10 visits on those websites it would work perfectly.
So i had to clear the cache/data of the web browser , reinstall the webbrowser , reinstall a lot of system components just to find out that this extension was the problem.

The UI is absolutely horrible, shows multiple scrollbars instead of scaling properly to fit the size of the pop-up. The buttons are confusing, there's no clear way of changing the UA of the current tab or resetting it to the browser default (you can only reset it for an entire "container," which is a collection of tabs users are rarely familiar with).

Doesn't work on most sites

Juste parceque j'attends que ce soit dispo sur Android

ERROR[No matching user-agent string for this query]

Первый раз перестало работать.

Useless. Does not work on https://music.apple.com/ running FF75 on windows 10.

This is first time with an Android phone

Not user friendly, Terrible UI. User Can't simply SAVE custom user-agent strings. for standard use, FAQ (its really a "FA-Q") must be read.

Doesn't seem to be designed for easy mobile use

Popup is now completely gone...

1.Requires permission to access data on all websites.
2.The pop up doesn't resize properly.

custom mode not work

I had an addong called useragent switcher before and this aint it! Wish I could find it. I don't know what to do in this current version. I used the button on the tool menu and selected a newer version of Firefox but when I click test it still shows my actual version--52.5 ESR and it doesn't fool the addons site when I try to install a new addon. So far none of the user agent addons are working, so adding to the list of fails.

The menu occasionally shows "recommendations" (ads!) for other add-ons that are not directly linked to the mozilla add-on page. This feels shady, and generally unsafe.

I feel uncomfortable using this add-on and have uninstalled it.