I have the same worry (although I have no evidence, and haven’t done much research into finding evidence).
I've slowly transitioned from FF to Chrome over the past year, for this reason. I still use both, but am trying to prepare myself for a time that comes when FF is no longer a viable primary browser.
Just going on what vulnerbilities that have been found (and assigned a CVE number) is one thing. The real question should be, how big is the real number of vulnerbilities that have not been found yet.
Looking at this from a pure CVE perspective, using Firefox rather than Chrome may reduce your exposure simply due to the fact that Firefox has a lower market share.
Is there a meaningful difference between the major browsers in terms of security? It’s hard to say to be honest!
Advertising networks are vectors for malware:
https://www.cisecurity.org/insights/blog/malvertising
https://www.malwarebytes.com/malvertising
https://theconversation.com/spyware-can-infect-your-phone-or...
Even the FBI recommends ad blockers:
https://www.ic3.gov/Media/Y2022/PSA221221?=8324278624
So if you're concerned about security then you want the browser with the best ad blocker.
uBlock Origin works best in Firefox:
https://github.com/gorhill/uBlock/wiki/uBlock-Origin-works-b...