I use this extension for many years now. But sadly the development is very slow. It's very outdated, you're stuck with very old and on many websites not anymore supported browser-versions to choose from like Firefox 134, Firefox 128 ESR, Safari 17, Edge 131. Also no matter which browser you choose from, on browserleaks.com/javascript its still possible to see that mozilla is used (the parameter appCodeName shows "Mozilla". So please ntninja update the extension!

Edit (2025.11.05):
In it's actual deprecated state this browser extension breaks the Cloudflare Bot Challenges.
If a website uses any of Cloudflares Anti-Bot Challenges it will break the website and render it useless.

Please add a redefinition for Yandex Browser (Window), because I'm tired of seeing annoying ads in Firefox every time I search!
PS: Windows / Yandex 25 [Desktop]: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:135.0) Gecko/20100101 Firefox/135.0 - didn't work

i use this to switch to linux to get windows iso

小心使用此插件，该插件可能会导致Cloudflare反复验证

非常感谢，它自由度高。

Thanks, I can see high quality Facebook Reels on Firefox because of this extension

doesnt keep itself isolated using "only for this site" pref. Apparently it enables selected UA for *all* sites, and for ones you didn't want you have to opt-out... Not best UX

Doesn't fool Netflix

Very usefully.

Plante instantanément Firefox mobile.
Instantly crashes Firefox mobile.

This used to be the most functional useragent-switcher (even if the UI/UX was left wanting), but even this doesn't seem to work anymore. 😕

Although this extension doesn't solve my issue completely (hating how Facebook looks and works), I am able to easily convince FB that my laptop is a mobile device which makes it more tolerable.