Yeah, this is a worry. Google or someone will just come up with some not needed but slightly better (from a mere feature perspective, not from a privacy one) thing, that websites will use. Lets say a new codec or protocol for something like ... VR in the browser! or similar stuff. That thing will be somehow easier to use with Chrome and they will call it a "standard". Then people will try to use those websites using it and ... Oh? You use FF? Too bad! It doesn't work there! But you could use this "modern" and "secure" browser, _made by Google_! (and half-informed people online will claim FF doesn't implement the "standard") ... and tada, the badly informed user switches away. Not to forget, when they install Chrome, they probably are asked to make it their default browser.
It is all quite dystopian and depressing to think about.
It's not only about big thingys. It's any small difference in behavior where some developer tests only on the browser with 90% usage* and ignores the small niche of Firefox users, leaving them accidentally with a broken site. Some CSS property, some JS API whatever.
*) The stats are somewhat wrong, I guess there are more Firefox users with different privacy blockers than Chrome, thus hiding from Google analytics and similar, which people use for stats in higher percentage
It is all quite dystopian and depressing to think about.