There shouldn't be any need to import the bookmarks and other personal data when you update.
Firefox should find and use the profile from the previous Firefox version without problems.

Did you reset Firefox or otherwise create a new profile?

• http://kb.mozillazine.org/Profile_Manager
• https://support.mozilla.org/kb/Managing+profiles

See also:

• http://kb.mozillazine.org/Recovering_a_missing_profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

You may also still have this data in the Time Machine if you use this.

• http://www.apple.com/support/timemachine/

Thanks for those tips, cor-el, but I couldn't find my profile data. The profile manager only shows one default profile, and I went wrong where I normally always import the existing settings when updating. I was just hoping there would be a way to get my old profile back which - with this one exception - I always kept by importing the settings when upgrading.

When you update you don't need to import, the built in updater automatically imports all your data, is it there?

Isn't that old data in the Firefox profile folder?

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• /Users/<user>/Library/Application Support/Firefox/Profiles/<profile>/

Tyler, No, it isn't, otherwise I wouldn't have lost it all of a sudden. I knew the 27.0.1 update was coming, and thinking back now I think this is what happened: I don't think it asked me about import, it just started the automatic import process (with compatibility check). This import process shows a dialogue on-screen, and I think when moving windows around I wasn't expecting that one to come up - as I did not initiate the update process and only very recently modified my preferences to automatically update instead of asking me first (I changed that back already). So I guess what happened is that I accidentally cancelled the automatic import process. So in that case my question is: Where can I find my pre-update profile?

cor-el, As you may have seen in my reply to Tyler, I think I puzzled together what actually happened: I may have accidentally cancelled the automatic import which is part of the upgrade process. And yes, I have found where my profiles are (menu 'Help', click 'Troubleshooting Information', then click 'Show in Finder' next to Profile Folder in the troubleshooting page), but I don't see any backups. I've been through https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from... and haven't found any pre-update info. Is that irrevocably destroyed after an update when cancelling the import?

There is no import window with updates. If you lost your data when you updated that is an issue, but there is no import process to cancel. Recover lost or missing Bookmarks

Tyler, so it seems I stick to just having lost my data. I have just reinstalled v27.0 and let it update to v27.0.1, and there is a window. I didn't see any profile import, which could be because I have no profile to speak of now. I do have a few add-ons, and these are checked for compatibility according to that window. Most of these add-ons have been running for at least the last 4 major & minor version updates and never caused any trouble. They were also all gone. So it looks like I didn't even accidentally click on something I shouldn't have, I just lost my information.

Did you verify that there is only one profile folder present and that is the one that you currently use?