Firefox is way too valuable as a hedge against Google hegemony to let die. If they ever lose the Google search money hose and become threatened I do expect a Google competitor to realize that and step in with some funding.

Microsoft basing Edge on Chromium was a really stupid move on their part for this reason, and I suspect they are starting to realize it.

That being said, I only expect it to be maintained at a hedge level, not enough to shoot for dominance again. Think of it like Valve's Steam on Linux efforts -- it's not a major effort on their part, it's just enough to keep Microsoft honest.