I actually use Chrome for everything Google, and Firefox for everything else. It's a constant reminder that I need to stop using Google services. I don't open it much anymore, just to check my gmail which still has a few emails going to it, and to find my android whenever I lose it.

Does gmail really not work in another browser like Firefox? Seriously? How is this possible?

It works fine in Firefox, I do it for the intentional isolation. To me, chrome browser is "google browser"

Almost everything runs just fine in Firefox.

Google software seems to be chrome-optimized, but it's usually only slightly slower on Firefox - it still works.

Some google websites are chrome only because of the use of some non standard plugins.

Do you have any details of which ones? I have not discovered any so far - everything seems to work just as well in Firefox (e.g. gmail, youtube, search, maps, adwords, adsense, analytics, cloud console, webmaster tools are the ones I requently use on Firefox with zero issues)

Google earth and Google hangouts

It works, but it uses non-standard extensions that are only present in Chrome, so it runs slow in Firefox, especially since their latest update.