Gregory's Server@downey Unfortunately the User Agent String is not the only method bad sites can use to block your browser.
The new "kid" on the block is the Client Hints Sec-CH-UA header (and corresponding JS APIs). I have seen one site exclude "unsupported browsers" and suspect another 3+, including a bank, of abusing the header, but can't test since if they are doing it, they are blocking after login.
For more about this, please see my article https://vivaldi.com/blog/technology/client-hints-or-client-lies/
@TechieNotNetie @downey this is fascinating, thank you. i have actually started seeing that error as well despite using a fully updated firefox; i suspected it was my scriptblocker for some reason and can only assume from your comment that i was right. interesting but frustrating.