Edge has a "feature" to auto-import data from other browsers every time it opens. You can check the status of that or turn it off from Edge: Settings -> Profiles -> Import browser data -> Import browsing data at each browser launch.

Thanks. Interesting. Just checked and it's not turned on and it's only an option for Chrome.

Then that would means your Firefox isn't the default Browser settings. And you need to also check that option to see if it's verified as the "Default Browser" in the settings of Firefox.