The Firefox Dilemma

With the news about Edge switching to a foundation using Chromium a lot of the conversation has centered on browser engines slipping into something of a monoculture. I believe these fears are coming from a good place - a monoculture certainly is not desirable, and a persistent challenge from competitors keeps tech at its best. Compounding this news was also a link floating around stating that Mozilla Firefox was staring at a market share of below 9%. What gives me pause, however, is that much of the advocacy for Firefox¹ seems to stem from the fact that it's not Chrome. The pure logic of such a strategy is clear, but is it particularly convincing as a technique?