To quote user tuna's review a day ago
"Firefox has not been able to start since the June 4 update."
I have the exact same problem and in order to make firefox start normally with the extension enabled, i have to start a private browsing session which opens two windows, one with one tab in private browsing and a second normal one with all the tabs that the extension has saved. Otherwise the apllication is killed almost immediately after starting with the extension enabled.