Look on your desktop. Do you see a folder called; '''Old Firefox?''' https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

<p>Let me expand on that a bit... Did you lose any Firefox data other than bookmarks, for example, passwords, history, add-ons?</p> <p>Data loss during an update is rare, but the most likely scenarios are:<br><br>(1) A Refresh occurred but the migration of data from your old profile to your new profile was incomplete, or<br>(2) Your old profile was locked, so Firefox ignored it and created a new one</p> <p>Here's how to investigate those two possibilities:</p> <p><em><strong>Did Firefox perform a Refresh?</strong></em></p> <p>Unless it was interrupted in progress, you should find a folder on your desktop named Old Firefox Data. Inside would be a semi-randomly-named folder with freshly updated files. Do you see anything like that?</p> <p><em>If not...</em></p> <p><em><strong>Does the Profile Manager list your immediately previous profile folder?</strong></em></p> <p>To check on that, inside Firefox, type or paste <strong>about:profiles</strong> in the address bar and press Enter/Return to load it. <br><br>This page should list all the profiles Firefox is currently aware of. If you see a profile that is not currently set as default that looks promising, scroll down to it and click the <strong>Set as default profile</strong> button below that profile, then scroll back up and click the <strong>Restart normally</strong> button. (There are some other buttons, but I think those are still "under construction" so please ignore them.)<br><br>Firefox should exit and then start up using the other profile. <em>Is that the right one?</em><br><br><em>If it's not there...</em></p> <p><em><strong>Did Firefox orphan your old profile folder?</strong></em></p> <p>Here's how to check whether there are additional profile folders in the standard location in addition to the one you're using. Start by opening your current Firefox profile folder using either:<br><br>* "3-bar" menu button &gt; "?" button &gt; Troubleshooting Information<br>* (menu bar) Help &gt; Troubleshooting Information<br>* type or paste about:support in the address bar and press Enter/Return<br><br>In the first table on the page, click:</p> <p>* Windows: the "Open Folder" button, to launch a new window listing various files and folders in Windows Explorer.<br>* Mac: the "Show in Finder" button, to launch a new window listing various files and folders in Finder.<br><br>In the Windows Explorer address bar, click the capitalized word Profiles to move up one level in the folder hierarchy. More than one folder here by any chance? Do the files in those folders look like they were last updated around the time of the update?</p> <p>(Mac users: please do what you need to do in Finder to check up one level...)</p> <p>If you've got any promising looking folders, we can discuss next steps to recover use of them.</p>