A quick example that comes to mind is The Great Suspender (the tracking-free community edition). Firefox’s alternatives were really not very good. (I’m not sure how it is now.)
What was really not very good about Firefox's alternatives to The Great Suspender? I read some opinions now. All but 1 recommended alternatives even in Chrome because The Great Suspender could lose tabs if the browser crashed. And tabs suspended with it couldn't be restored without it. The other preferred The Great Suspender because it let them activate a tab without loading it.
But the question was why Chrome beat out Firefox the way that it did. I think Chrome overtook Firefox before Chrome extensions overtook Firefox extensions.