I think one of two possible scenarios will occur
1. Firefox fades into obscurity/irrelevance, Chromium becomes the platform of the web, and thus Google dictates its future.
2. Firefox fades into obscurity/irrelevance, and Chromium still becomes the platform of the web, but anti-trust action is taken against Google with a result being that Chrome is spun off into its own entity independent of Google, and so while there's still a browser monoculture, that browser is developed by a relatively unbiased company.
Of course in all of this there's always the foothold that Safari has that must be taken into consideration, particularly on iOS where users quite literally don't have the choice to use another browser (as iOS Chrome and friends still use WebKit under the hood).