Portable apps should not be added to Windows Shell default programs via their own menu or settings, as this may break things.
If you like myself are fucking tired of Firefox blocking vulnerable extensions – in fact it does that each time a new plugin version update appears, and you have to reinstall them again and again.
Download from here. So you want a portable browser on your Mac?
Firefox keeps being updated, and some updates are just plain stupid.
This connection is untrusted.