Well, I upgraded to the beta, and I still have the same problem with the Lastpass extension: it needs re-enabling each time I start the browser. Frustrating...
Have you tried uninstalling and reinstalling it?
I back-up Ayespy on that one. When the extensions weren't officially supported (like in February-March), I had to uninstall-reinstall after many snapshots because extensions were reinitialized all the time
I had the same problem as the thread starter and de- and reinstalling the extension worked for me.
Have a nice day!