good gan...

It's fairly good, but it has some big issues:

(0) *** It needs to allow per-site overrides. You should be able to set a global user-agent string, but override it with a different one for specific sites. ***

(1) It doesn't get regular updates to keep the user-agent string up-to-date with new browser versions.

(2) If you modify the string of a combination of OS+browser, there is no way to reset it to the default, and the change will be retained even if uninstalling and reinstalling.

(3) No option to save a custom string; if you change the agent, the custom string is lost.

(4) No option for random agent.

It's not work on Firefox for Android

he很不错

it's interface is easy and friendly, but you have to update UA strings because many websites break and say that my browser is old and not supported, which makes the addon useless.

Toolbar button does not appear. I tried both restarting and reinstalling. I'm using FF 68.0a1.

Compatible with Waterfox! It's very easy to use and the interface is nice. Editing doesn't allow to change the agent icon, but the strings may be freely modified (you may input a Safari string in an IE option). It has a site filter, but it's global, not individualised for each agent (that is, there can't be different UA for different sites).

No option to whitelist sites