Firefox > Bookmarks > Show All Bookmarks ( or <Shift><Control> B ). At the top of the window, select Import / Backup, then Restore. You should then see a menu of saved bookmarks.

When you reset Firefox then a new profile is created and some personal data (bookmarks, history, cookies, passwords, form data) is automatically imported and the current profile folder will be moved to the desktop to an "Old Firefox Data" folder.
Installed extensions and other customizations (toolbars, prefs) that you have made are lost and need to be redone.

It is possible to recover more data from the old profile, but be cautious not to copy corrupted files to avoid carrying over the problem.

• https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox