If chromium were abandoned they wouldn't really have a choice, would they? I guess they could migrate edge to run on top of firefox, but I'm not sure if they'd

If chromium were abandoned they wouldn't really have a choice, would they? I guess they could migrate edge to run on top of firefox, but I'm not sure if they'd want to. It's actually a little interesting, why did they choose Chromium in the first place over firefox, when Microsoft and Google are more directly competitors?