(I remember posting this before, but I am unable to find it anywhere. Perhaps it wasn't stored. I apologize in advance for duplicate posting!) I use Firefox 75.0 (64-bits) on mac OS X Catalina for browsing. It gives me the following issue. When I start typing a youtube… URL in the address bar, a specific sub-page to the YouTube domain pops up first. It refers to s specific clip on youtube. While I’m typing, in front of it a grey star appears, such a marking a favorite. However, it’s NOT in my favorites. The auto-suggestions do not come from other opened tabs. This option is turned off. 
I don’t use any Firefox subscription account services for storing favorites online. Suggestions from search engines are also toggled off. 
I’ve tried all remaining suggestions on the following pages to get rid of this issue: https://support.mozilla.org/en-US/kb/remove-websites-address-bar-suggestions 1st method for clearing a single item didn’t work; 3rd method to clear my browsing history didn’t work. https://support.mozilla.org/en-US/questions/1213978 I have turned off browser.urlbar.autoFill = false. Toggling this option, at least, got rid of unsolicited suggestions from the worldwide web such as youtubemoneycalculator.com. It’s a partial success! https://support.mozilla.org/en-US/questions/1213978 keyword.enabled is set to false, but toggling this won’t make any difference. browser.fixup.alternate.enabled is set to false, but toggling this won’t make any difference. The only method that makes a difference is to turn off Addres bar suggestions from Favorites (in about:preferences#privacy). But then I don’t get any suggestions at all… This example merely illustrates the issue with youtube… domain names, it happens with any address that I start typing in the address bar. Peculiarly, addresses that ARE stored in my favorites, do not appear first in the suggested domain names.
Okay, I’ve done my homework! My conclusion/question: Some (former) favorites are stored in a location that I have no access to. I would like to receive suggestions as to where I can find these. Preferably, I do not want to delete every single one of them one by one. Bottom line: It would be nice if I had some sort of control over my favorites. The suggestions appear to be totally random. If the most recently or most frequently visited favorites would appear first, that would make sense. Or if the main page would appear first (youtube.com) and not any other subpages. Does anyone know if this is possible and then, how to achieve this? Lastly: I don’t understand why a browser that claims to be so concerned about my privacy allows for so many unwanted options. Also, it is a nuisance if these options are actually reset with every update Firefox installs. I have the impression that this happens. I did notice that now and then additional search engines are added to my one-click-search engines (about:preferences#search) without my prior notification. How does this comply with Firefox’s privacy concerns?