Why is LastPass add-on frequently disabled because it is "unverified"?
Several times a week, when I open Firefox it tells me that the LastPass add-on is "unverified" and disabled. I have to go to Mozilla's Add-on webpage and re-install it. It cannot be "unverified" because I install it from Mozilla's installation list. Many people are having this problem: https://forums.lastpass.com/search.php?keywords=firefox+unverified&terms=all&author=&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search
Why is this happening?
Opaite Mbohovái (1)
Sounds that something is blocking Firefox from checking on the AMO server whether the extension is still present. Current Firefox releases will regularly perform a check to verify that all extensions are still correctly signed. If this check fails then the extension will be blocked. The latter appears to be happening in your case.
Make sure that your security software isn't blocking these checks to verify the status. I don't think that the update settings in "Options/Preferences - > Advanced -> Updates" would have effect.