I really like the blacklist & white list features. however every time I press save, all my settings are lost

It simply does what it is supposed to do. It would be nice if it was possible to change the user agent automatically at predefined time intervals.

Works as advertised :)

别用排名第一第二的useragent插件了
这个最牛B了
首先多，各平台各新旧版本
再来就是黑名单白名单自定义规则太强大

来使用百度简单搜索APP的useragent来访问百毒看看
Mozilla/5.0 (Linux; Android 7.0; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/48.0.2564.116 Mobile Safari/537.36 T7/10.3 SearchCraft/2.6.2 (Baidu; P1 7.0)

これから楽しみです。他のブラウザでは楽しんでいます。

Opens a tab at the far right containing a webpage asking for money(donations), then shows google ads in there.

すごく良い
非常に見やすいUIで、メジャーなOSはほとんど揃っていて、ブラウザも最新ブラウザでない限りある程度揃っている。
直接編集も可能
javascriptにもちゃんとカスタムUAが聞いている強力なUAスイッチャーです。

Nice extension, can switch what i use now to diffrent

This appears to be an effective agent switcher, I like it but there's just one thing, I can't set the screen resolution to something different than what my actual screen resolution is. If you could add in an option for spoofing the screen resolution this would be a 5/5 add-on :-)

Minimal, under 1 MB (not like other extensions which can be up to 8 MB for no reason). Works as expected, great UI. Thank you for developing this, it's a far better option to the more popular extensions.

I love this add-on!
With the recent onset of Apple enforcing its "proprietary" right to use the emojis we are all used to, Slack, et al were forced to switch to their own, non-Apple Color Emoji typeface -- and if you're like me, they're HIDEOUS emojis. This extension allows me to permanently spoof the user agent to an iOS device for specific sites where I use emojis a lot. Like Slack, fb, etc.
When I was using Chrome browser, I could only achieve this by CTRL+I and de-toggling "Select automatically" under the Network Conditions sub-menu inside dev tools. So this permanent fix in Firefox is exactly what I wanted.