Upgraded to Firefox 151.0.1 and all my bookmarks are gone.

Hello, First, you can see if it has switched your profile. To check, type about:profiles, and see if there is an old profile in there, and launch the profile. If the bookmarks appear, set the profile as default. If not, proceed to the next option. You can also try restoring from the file directory. First, press Ctrl + shift + 0 (or Cmd + shift + 0 for Mac), then click import and backup, then select restore>choose file, then find the desired file in the bookmarkbackups folder, which is usually located in your profile folder, then open it. The manual way is typing win + r, and putting C:\Users\YourUsername\AppData\Roaming\Mozilla\Firefox\Profiles\YourProfileName\bookmarkbackups\. (yourprofilename/username is just placeholder for your real username or profile). after you found it, you can find backups there.