Does not work – user agent stays the same.

It works. It works well BUT it floods ADs, some precede videos in sites - bombarded with useless, bogus ads - SHOVING them. As much as I like being able to easily present a browser change, the issue still remains.

CPU heavy, and when using isolated tabs, you have issues, it wont go BROWSER WIDE... you have to set per tab n stuff, its a PAI, and ive heard the dev has shut up shop and its full of bugs

Mozilla need to re-review this and give the golden cup to another user agent that can be trusted!

Aside from the white and black lists, this extension also has a list of domains where the UA should never be spoofed. It's never stated that it exists, and I found it out only when I accidentally opened the settings. This list includes domains I was using this extension for, which means that my UA wasn't actually spoofed there. 1/5, many thanks for a privacy leakage for no apparent reason.

it is difficult to master - you need a simple GUI option, where each site offers its own identifier, and not offer to write in a scripting language.
and of course the fox starts using the processor from 1.5% to 15%.

The modified browser profile does not pass Cloudflare's validation. https://webbrowsertools.com/ip address/

With extension enabled all the sites that use Cloudflare are don't load. Which makes this extension pretty much useless. I hope this issue get fixed then i will change my review.
Edit: Another review reminded me that it "makes the CPU go nuts every 30 seconds!"