Each of these methods installs in a separate location - no conflicts should exist from a package standpoint.
You may find that the configuration files are shared, which I imagine could cause issues if the versions are different (new functionality in config files that isn’t supported in an older version, for example). Haven’t heard of any issues with that, but it’s something to be aware of as a possibility.
Firefox settings are stored in profiles.
If you will use different profiles for different installations - then they will coexist.
I’m using Firefox + Firefox ESR from openSUSE’s Mozilla repo, ant they work OK.
Another possibility - use tar from Mozilla.