Is this what you did?

Look on your desktop. Do you see a folder called; Old Firefox? Look inside. Look for the folder with the latest creation date.

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

Sorry either I didn't understand this or it didn't work. Specifically looking to bring the onetab extension history over. Not sure where they are in the "old firefox data" folder. Tried session store backups that didn't seem to work, and then tried pulling the onetab xpi file over and that didn't work. Is there another one in there I'm missing, maybe one of the many xpi at the top of the extensions folder?

For that, you should ask One Tab support.

Unfortunately, it's a bit of a treasure hunt because extension storage folders are named using a unique local ID that is going to be different in your new profile.

Let me see whether I can find the folder for you.

First, inside your Old Firefox Data folder, inside your old profile folder, there is a file named prefs.js containing a long line that correlates the basic extension ID with the unique local ID. Since this is a script file, please do not double-click it as that may execute it. Instead, right-click (one button: Ctrl+click) it and open it in an editor such as TextEdit.

Note: we are just doing research here, we aren't going to save any changes.

Use your editor's find function to look for extension@one-tab.com

You should find something like

... \"extension@one-tab.com\":\"a7e6b610-c93b-4b0b-9128-95debea705e9\", ...

The number following the :\" is what you will use to find the OneTab storage folder.

So in your profile folder, look here:

Old Firefox Data/[profile.folder]/storage/default/moz-extension+++[local unique ID]

Sometimes that is followed by ^ and a context ID

That is OneTab's data folder. As for how best to use it in your new installation, I'm not sure. I suggest checking with the extension's author on that.

One other note:

Were you able to restore your tabs from Firefox's built-in session history (Restore Previous Session)? If not, and you don't erase history when Firefox closes, you can at least extract those out as a clickable list.

Look for any of these files:

• Old Firefox Data/[profile.folder]/sessionstore.jsonlz4
• Old Firefox Data/[profile.folder]/sessionstore-backups/recovery.jsonlz4
• Old Firefox Data/[profile.folder]/sessionstore-backups/recovery.baklz4
• Old Firefox Data/[profile.folder]/sessionstore-backups/previous.jsonlz4 -- earlier session

And my converter is over here:

https://www.jeffersonscher.com/ffu/scrounger.html

After dropping the file in, click the Scrounge URLs button. If it gives you useful results, click the Save List button to archive the HTML page to your computer for future reference.

So was able to find the onetab extension info, but if you're unsure how how to implement I'm equally unaware. That said, not 100% sure if I got everything but the export to scrounger from the previous "old firefox" folder seems to have pulled up a lot of the links, if not all of them. So THANK YOU!! Hopefully last one this did the trick!

Later edit - turns out it didn't totally fix everything, just had a bunch of links show up from earlier in the day. Reached out to onetab, maybe they can help.

Note that the OneTab extension has an import/export feature, so best is to use this feature to prevent future data loss.

See the import/export now, which I would do if I knew things were going to get removed, but didn't know beforehand it wouldn't. Thought just pulling everything into onetab would work, but didn't.

Thank you for your hints on how to restore the tabs from the session history, it really helped :-)

As of the extension@one-tab.com : I have found both the old archived OneTab's data folder and the current one. I have tried to copy (replace) the current files (backuping them to some place for sure) by the files from the old archive (while FF was closed). This does not work (the One-tab extension does not work then). Copying the current files back from the backup restored One-tab extension to work, but not with the old items.

Does anybody know how to restore the old items ? Or possibly how to open the \idb\3647222921wleabcEoxlt-eengsairo.sqlite file for editing (as obviously this file has the old archived OneTab's info we need to recover). Thank you.