You get this error if the profile the last time has been used with a newer Firefox version. You can check compatibility.ini in a profile folder to see that Firefox version and installation path last used this profile.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Primary location used for the main profile in the hidden "AppData\Roaming" location that keeps your personal data (Root Directory on about:profiles).

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>

That's why I specified that I am using the ESR profile and it is the only folder actually in existence at that location. So if it's that I have no idea what it's actually trying to load and would love some help figuring that out

Could you check the Windows Task Scheduler and see whether there are any Firefox tasks -- such as the update checker or default browser checker -- that run with a specific profile specified? It's probably safe to delete those tasks and let the next update re-add them with updated paths.

Took a look and don't see anything Firefox related in the task scheduler. Just a bunch of NVIDIA and some edge updates

It's possible that they only show in the Mozilla category.

That was it, thank you!

Cool. If something still triggers the error at startup, then I would try the Microsoft Sysinternals program "Autoruns" to track it down:

https://learn.microsoft.com/en-us/sysinternals/downloads/autoruns