I'm very surprised that Chrome can access any Firefox data. (Firefox Sync only works between Firefox installations.)

As am I. I did import my bookmarks from chrome when I initially installed Firefox so I’m wondering if there was a checkbox somewhere in that process that indicated I wanted them synced.

Hi

There is no way to sync bookmarks between Firefox and Chrome, but do you by any chance use the same user name and password?

When I installed Firefox it asked if I wanted to import bookmarks and the like from Chrome, which I did. But my Mozilla account uses a completely different, non-Gmail email address so there shouldn’t be any crossover on account of that. How my Google search history from Firefox is showing up in chrome even though I’m not signed into a Google account on Firefox is beyond me. Definitely a chin scratcher

This isn't really relevant to the Sync question, but if you go to Google in a private window (Ctrl+Shift+P) and search there, is that activity at least hidden from Google history on Chrome?

Yes, in private (Incognito mode) the previous search history is not visible

Actually, I am trying to complete the picture for #2

(1) In Firefox, regular window

• Search on Google site while signed out of Google account
• Expected result: Queries submitted to Google should not be added to web activity for your account because you are signed out
• Actual result: In Chrome, signed in to Google, queries submitted in Firefox are visible (seems possible only via web activity, so WTF) because REASONS TBD

(2) In Firefox, private window

• Search on Google site while signed out of Google account
• Expected result: Queries submitted to Google should not be added to web activity and therefore should not be visible on Google site in Chrome because you are signed out AND ALSO use of a private window prevents Firefox from sending Google any cookies previously set by Google in regular windows that might connect the signed out session to your account
• Actual result: In Chrome, signed in to Google, queries submitted in Firefox are... TEST PENDING

Well now that's interesting - now it seems to have stopped. In Firefox I used Google to search for "best skateboards." A valid test since I never have and probably never will actually want to see those results. At this point it is not being reflected in my search history for Chrome. So now we have a case of a computer behaving differently under the same circumstances. Very strange but such is the way with computers. Happy to run further tests if you're curious but it seems to have fixed itself 🤷🏼‍♂️

Ugh. I figured it out - I had installed Vivaldi to try it out and for some reason signed into my google account there so that's how it was cross-pollinating into Chrome. Problem solved. Well...more like I figured out what happened, I think the problem may still remain in my internal memory 🤦🏼‍♂️