I was originally an Opera user (back when it was using Presto) back in the day, but I switched to Firefox during the last moments of the Presto engine. When Presto died, I worried a bit about the state of other browser engines, but I didn't worry about it too much because I never thought Microsoft would use Chromium with their Edge browser. Yet, here we are.
Putting privacy concerns aside, we should encourage the use of Firefox because it helps promote browser engine diversity. The more diverse browser engines we have, the better it is for us, especially when it comes to innovation. I mean, it may be a bit different than the era of Internet Explorer, but since Google is leading the Chromium project, who knows what could happen.
They might remove a particular feature that was once very useful for whatever reason, and we could end up just accepting it because we can't do anything about it.