Still typing in FF 52.9, I have been working on my 2 Busters and those are 60.3 now waiting for 60.5. I've dug into about:config and have been watching that. I have changed 3 dozen things. There are details here to notice.
First, thank you FF. Past settings are conserved through upgrades.
If you use nightlies or other non-distro-repository install techniques you can loose that. This round I have noticed a handful of my changes are not needed with Debian's official release. The kind dev's there have a few settings locked, already on the setting I'd choose. My guess on a downloaded version ran in user space sandbaoxed or whatever is fully OS/HAL probing enabled, and fully telemetry-ized, enabled experiments opted-in, etc.
While I use no extras, I do tweak. FF does seem to dribble the least.