Win 10 desktop startup issue

Upgraded to Win 10 a couple of months ago on Toshiba laptop.

All was well until about 3 weeks or so ago, after an OS update. Windows will still startup to the desktop however a couple of seconds after the desktop screen appears, the default browser (Firefox in this case but did not matter which one is checked as default - have Edge, Chrome and FireFox) opens to an MSN homepage. Not really a HUGE problem as I can click and close it out but it is just an annoying issue. Have been virtually everywhere in the system and cannot find anything that will stop this. Have checked plugins, searched for malware, looked at task and startup manager and can find nothing that will stop.

Any help / ideas would be appreciated.

Have you checked out Task Scheduler?

Or Users\username\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Start-up? (Talk about well buried!).

No, did not even know that existed. It sure is buried. Did not find anything there although honestly, I could not really figure out what some items there were.

Maybe you should record here what is in startup?

There are two registry locations that should be checked as well.
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
And the same again except it starts with HKCU (HKEY_CURRENT_USER)