pkg(8) takes an aggressive stance to ensure everything is consistent. If it needs to update something that was likely a dependency of Firefox but as in this case Firefox was unavailable, it will end up removing Firefox since it can't keep the dependencies in a consistent state. If anything, always keep an eye on what it says it will do during the upgrade and say no if you don't agree with what it is about to install or remove.
pkg upgrade when it wasn't available in the remote repository for whatever reason.Thanks kpa. What I was going for is if on of Firefox's dependencies needed to be updated and if that would have resulted in a reinstall of Firefox due to a shared library change that it could have resulted in this. My word choice wasn't very clear.This holds for ports that are required by other ports but Firefox is a "leaf" port and not required by anything else. I highly doubt that the removal was a result of dependency conflict but something else. Specifically I've never seen a leaf port removed bypkg upgradewhen it wasn't available in the remote repository for whatever reason.