Is there any advantage to using the latest firefox version by itself vs the firefox esr version included with leap 15.2?
Newer versions are as likely to have disadvantages as advantages, as for the past few years the upstream developers seem to have been more focused on weight reduction and Chrome emulation than anything else. If you want a more specific answer, the right place to go is to the release notes on mozilla.org, to see the list of changes.
Ok. I’m good as long as the esr gets all the security updates.
Newer versions of a FF gives speed enhancements - Webrender, WebGPU, etc.
But hardware upgrade provides much more speedup.