I never had a lot of difference between both browsers (never got to use chrome much, admittedly), but even when it was supposedly "bad", Firefox never struck me as being especially slow.
I definitely noticed, before quantum (like 5 years ago) single page apps and frameworks like react were becoming a thing, and it was noticeably less snappy than chrome
After they announced the rewrite to better handle shadow doms and partial repaints, I switched for everything but development
Since then, they've done another rewrite, and the dev tools are closer, so I only open chrome when a site I have to use isn't working, or by client request
The Firefox team made some announcement about the performance improvements so I gave it another shot and found they weren’t joking around. On ‘slow’ work-issued computers (especially with spinning rust drives) - Chrome was snappier. This was experienced mainly on Debian and MacOS. I switched over completely after this v3 insanity was announced so it was like night and day for me.