try clicking "refresh firefox" in help > troubleshooting information. this generally helps a lot with the performance/settings and leftovers from previous versions. it acts as a factory reset. generally refreshing firefox does more then the re-installation process itself in terms of cleaning data. for restoring add-on and bookmarks, i recommend using firefox sync before refreshing firefox.
also, i highly recommend using secure login instead since it acts as a extension to firefox's password manager and enables login with a click of a button. lastpass is way more complicated and memory-consuming as a add-on than it needs be as compared to secure login.