Sometimes this happens when Firefox starts up slowing after the upgrade and shows a button to speed up the browser by restoring some default settings. If you click that button, the Refresh feature runs, moving your old settings folder to the desktop inside an Old Firefox Data folder. Do you see anything like that? Otherwise, could you post a list of your current set of extensions? It's easiest to copy from the support information page. Either: * "3-bar" menu button > "?" button > Troubleshooting Information * (menu bar) Help > Troubleshooting Information * type or paste about:support in the address bar and press Enter Scroll down to the Extensions heading, use the mouse to select from there through the table that follows and copy (e.g., Ctrl+c or right-click > Copy) and then paste into a reply (e.g., Ctrl+v or right-click > Paste). It will look a little messy, but don't worry, we're used to it.