Technical post here. I noticed this obnoxious combination while using Firefox on Windows 10 recently (within the past week).
Some background: I have Windows 10 installed on my main PC along with Mozilla Firefox (latest version). Microsoft’s new browser, Edge, is sitting in my quick launch along with Firefox. I have “Get tips, tricks and suggestions as you use Windows” enabled in Windows Settings.
I started Firefox from a cold start and was presented with this:
Evidently Windows uses the same methods as assistive technology screen readers (such as those for blind users) to determine if Firefox has been launched, and, if so, presents you with its little ad for Edge.
Note that this does not interfere with Firefox working normally, only its in-testing multithreading system. If this aggravates you, you can remove Edge from the quick launch bar and/or disable these ads altogether in Windows Settings (search for “tip”).
According to Mozilla, this will be fixed eventually.