The bug that is mentioned here wasn't the problem. I am running on FireFox 60 ESR so I'm not subject to bugs that are in FireFox 64 and I still had this problem. Plus that "bug notice" clearly goes on to state that the person reporting the bug couldn't reproduce without having LastPass 184.108.40.206 installed and having LastPass 220.127.116.11 installed didn't see the issue. So LastPass was trying to misdirect you to say it wasn't them but it clearly was something in their updated version.
That being said now that LastPass has finally updated and are on 18.104.22.168 I am noticing the issue has mostly gone away. I still have some slowness issues on a couple pages but I no longer get warnings from FireFox that a script in LastPass is slowing things down.
I hope everyone else is seeing this as resolved now as well with the new version released today.