Yes, I agree that some Firefox users had moved to Chrome early on, and that Google does have the potential to market Chrome more forcefully than Mozilla can for

Yes, I agree that some Firefox users had moved to Chrome early on, and that Google does have the potential to market Chrome more forcefully than Mozilla can for Firefox. I don't think that the timing is all that relevant, though. This has been a gradual process over several years now. The main point is that it wasn't so much what the other browsers and their vendors did that reduced Mozilla's influence, but rather that it was what Mozilla did (or didn't) do that has resulted in Firefox's decline. Mozilla stopped leading, and instead decided to follow Chrome. While doing this, they've bungled major Firefox features, ranging from automatic upgrades to the UI design, time and time again. They've neglected to sufficiently resolve long-standing resource usage problems. They've ignored feedback from disappointed Firefox users for years now. They've ignored that this direction obviously isn't helping to prevent users from leaving Firefox, while at the same time it's driving a lot of users away, and furthermore it isn't really bringing in any new users. In my opinion, Mozilla has been its own worst enemy these past several years. They've inflicted more harm on their own cause than any external opponent or competitor could have ever hoped to do.