This really has nothing to do with Intune. All Intune can do is run a command line that you provide against a set of source files. What that command line is up to the author of the code that the command line runs and is completely outside the scope of control or visibility of Intune. Thus, whether or not Firefox auto-updates and how it does so is up to Mozilla and not Intune. If Mozilla has provided a channel to control Firefox via registry values, scripts, file changes, an ADMX or anything similar, then conceivably, you could use Intune to control this behavior but by default, Intune in no way knows how to control any random app (no matter how popular that app may be).
The information provided by @Nick Hogarth may get you started here, but keep in mind as noted, this is specific to Firefox and not Intune.