Uh-oh, when you sign into your Firefox Account and you have Sync enabled, Firefox synchronizes the data in your account with the locally stored data; they should end up being combined.

Question: Does anyone else use this computer and would they mind if you zap all the data?

If you are free to zap it, you can create a new profile. This sounds like a lot of steps, but it's quicker than cleaning out individual data buckets:

(1) Create a new Firefox profile for this computer

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 the profile with mixed data that you will delete in a later step.

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

If you see a "Set as default profile" button for October, go ahead and click that, but Firefox usually takes care of that automatically.

(2) Start Firefox in the new profile and open its about:profiles page

On the about:profiles page, click the Launch profile in new browser button for October.

Firefox should open a new window that looks like a brand new, uncustomized installation. Don't log in.

Type or paste about:profiles in the address bar and press Enter/Return to load it. You should see both the mixed profile and the October profile are indicated as being in use.

(3) Close out of the mixed profile

Switch windows and close the mixed up Firefox. Then reload (click the Reload button, or F5 or Ctrl+r) the about:profiles page in the October profile. The in-use message should be gone for the mixed profile.

(4) Remove the mixed up profile

Below the mixed profile, click the Remove button. Choose the option to remove the data files.

You're done. If you exit Firefox and start it up again, it should seamlessly use the new profile.

The browser information that I'm looking at is not mixed in with the browser information for this computer; it's only my personal information, folders, etc., not what I had on this computer. I made sure not to click on sync.

So I'm not sure what you want to do at this point.

Do you want to run a clean profile of Firefox that doesn't have the information you see currently, but leave what you see currently as it is?