One of Chrome's big advantages over Firefox is they're much less skittish about telemetry, so Chrome devs can spend their time optimizing the exact scenarios that people experience. Firefox devs have to guess which things need optimizing, so even if they make something 100× faster than Chrome, if it turns out that particular circumstance doesn't show up very much, that's wasted effort.

It's pretty frustrating to read comments on HN or wherever that say things like "I like Firefox's stance on privacy, but it just never feels as snappy as Chrome".