It would have been interesting to see how things would have turned out had Microsoft been able to continue integrating the OS and web browser.
At this point I expect most users expect the OS to include a web browser and would consider it deficient otherwise. I'm not sure if it's even possible to replace Chrome with Firefox on ChromeOS.
You can install Firefox on ChromeOS. (At least I've done it on ChromeOS Flex.) However, just like Windows 98 used Internet Explorer for some of its internals (eg the 'live' Desktop), so does ChromeOS use Chrome for eg tweaking the settings.
It would have been interesting to see how things would have turned out had Microsoft been able to continue integrating the OS and web browser.
At this point I expect most users expect the OS to include a web browser and would consider it deficient otherwise. I'm not sure if it's even possible to replace Chrome with Firefox on ChromeOS.