Unfortunately there is no simple method and, the workaround is far from perfect. The .json files Firefox uses overwite the existing bookmarks but the .html option appends and does not overwrite. First of all backup all bookmarks on each hard drive. The best method of doing that is to backup the Firefox profiles, that captures the bookmarks databases (''places.sqlite'') and the autobackups that Firefox holds. * [[Back up and restore information in Firefox profiles]] * [[Restore bookmarks from backup or move them to another computer]] #First ensure you have the largest databsae on the current install of Firefox. If necessary ##Locate the Firefox Profile on the old drive ##* [[Profiles - Where Firefox stores your bookmarks, passwords and other user data]] ##Open Firefox and find the profile that is currently in use. ##*Quick method <br/>Use FirefoxButton -> Help -> Troubleshooting Information [Open Folder] <br />(No certain of exact wordings, OR navigate to ''about:support'' ) ##* [[Back up and restore information in Firefox profiles]] #Now use HTML backups to transfer from the smaller database the basic bookmarks. ## Close Firefox & if the old database is the largest one use the Operating System copy option to overwrite the existing places.sqlite so that Firefox now uses the old database ## Reopen Firefox but this time open using the old profile. The easiest method of that may be to disable the new drive from the Bios or alternatively use Firefox profile manager and register the old profile location and open firefox with that profile ##* [[Use the Profile Manager to create and remove Firefox profiles]] ## Export the bookmarks from the old profile using the Firefox Library and the HTML option. ##* see [[Export Firefox bookmarks to an HTML file to back up or transfer bookmarks]] ## Close Firefox, reopen new version/newprofile and import the HTML. You now have the largest database of complete bookmarks with tags etc. , plus additional bookmarks from the smaller database added on. Obviously you may have some duplication