For anyone who's done all the troubleshooting steps (disabling add-ons, confirming preferences, reinstalling the extension and Firefox, ensuring cookies are on, ensuring auto log-off isn't enabled, etc.), but still has this issue, LastPass Support has confirmed there's an "ongoing report", whatever severity that is.
You've reached LastPass Support! We’d be glad to assist you accordingly.
Upon checking, there is currently an ongoing report about this issue. We have yet to see any further resolution from the Development / technical team. But rest assured that they are doing their best to resolve this issue the soonest possible time. I will add your occurrence to the internal report, so our Development team will be alerted and to add severity to the ongoing issue.
Since we're not able to state when this will be addressed, kindly track the extension releases here https://lastpass.com/upgrade.php?fromwe ... asenotes=1
I would also like to add that our system may close this ticket in a few days automatically, with an automated message that you can feel free to disregard, Have a good day!
All the best,
FWIW, I'm on Firefox 59.0.2 & LastPass 4.9.0. The link given is quite old, so I've asked Martha for a proper link. I had this issue, some of the troubleshooting steps worked, but now it's appeared on its own again.