This morning Firefox put out a update, after I installed it, Lastpass started working again thru the Add On. For the last 5 days it had not worked. I dont know if it was a Lastpass update or a Firefox update, but this has happened in the past too. I love the security of it and Ive used it for years. BUT they really should test out the Add On before they release it.

I've used the paid version of this app since 2017. It's now pretty much flawless.

If Firefox has the following settings, you will get an "An unknown error occurred" error when you try to log in to Lastpass.
History Firefox will Never Remember history

If Firefox has the following settings, you can log in without any error.
History Firefox will Remember history

Firefox 81.0
Lastpass 4.56.1.3

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I can now log in after updating to Lastpass version 4.57.2.5 (September 28, 2020).

I have loved it and recommended it, and after a brief hiccup, I love it again.

Login Bug fixed in 82.0a