I can't seem to add this add-ons , what'd the solution

This random user agent is not highlighting what do I do

it good but it ain't allowing me to add it

Don't use it for privacy.

Does NOT pass this test : https://webbrowsertools.com/useragent/
See "[aggressive] iframe navigator.userAgent" test

Canvasblocker pass it without any issue.
And Random user agent isn't open source.