Since a couple days ago, on certain websites (like tweetdeck) Firefox reports every 5-10 minutes that a script in the extension lastpass is causing Firefox to slowdown, and then the page hangs for a few to many 10s of seconds. It even happened on this page as I try to type this in. This never happened, until the lastpass extension apparently updated last week.
About lastpass reports.
Built: Wed Dec 12 2018 20:54:08 GMT+0000 (UTC)
Binary Component: true (Native Messaging version 4.1.59, built Aug 13 2018 06:30:28)