It didn't disappear, it just turned into a tiny icon on the URL bar (everything bar?) with the temperature in a bright, unreadable yellow, or was it green?, that hid the icon. I discovered that was it, have to click the icon, no more display on the add-on bar (using CTR for years), had to revert to version 2.4.8 to get it back. I hope version 4.1 provides the functionality and options I am used to, if I'm still using FireFox in November. Mozilla just keeps on taking away more options with a lot of the updates, I'm thinking of going back to Seamonkey. Maybe try PaleMoon, if it will download correctly this time. Firefox is turning into Chrome and I don't like Chrome.