Technically you can't merge account as no one here that has access to your account except the user. If you login on the same browser the data could merge but if one logs off either accounts the data would be removed as it doesn't match the account it was synced to.

Just to clarify, you have two accounts linked to two different email addresses?

So you are currently signed in to and syncing with one of those accounts, but you want to see/extract the data in the second account?

I agree with your idea to create a separate profile linked to the second account. There is no built-in method to merge history, but at least you'll have the option to export/import bookmarks and saved logins. There probably will be duplicates that need to be cleaned up manually (or with the help of an add-on) if you import.

New Profile

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Take a quick glance at the page and make a mental note of which Profile has this notation: This is the profile in use and it cannot be deleted. That is your current default profile.

Click the "Create a New Profile" button, then click Next. Assign a name like OldAccount, ignore the option to relocate the profile folder, and click the Finish button.

Firefox will switch your default profile to the new one, so click the Set as Default Profile button for your regular one to avoid an unwanted surprise at your next startup.

Scroll down to OldAccount and click its Launch profile in new browser button.

Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.)

Please ignore any tabs enticing you to import data from another browser and sign in to your old Mozilla account. You may need to leave this window idle for a couple of hours to make sure that Sync completes.

Before you leave, I suggest setting a different theme so you can tell at a glance which windows belong to which profile. See: Use themes to change the look of Firefox.

After Sync completes, see these articles for exporting:

• Export Firefox bookmarks to an HTML file to back up or transfer bookmarks
• Export login data from Firefox

And in your main profile, these articles for importing:

• Import Bookmarks from an HTML file
• Import login and password data from a file

When you are done with OldAccount, you can close the extra window without affecting your regular Firefox profile. It will remain available for future research needs.

When you rebranded the Firefox accounts to Mozilla accounts (or maybe during the close of relay??) I accidentally created a second account.

The name change from Firefox Accounts to Mozilla Accounts (the only thing that changed) occurred back in early November 2023 to reflect that it is no longer used just for Firefox Sync and the Account is used for multiple Mozilla services now.