Nowadays if a site does this I simply don't visit it. If it's a really important site (which often does support FF anyway), I just use Edge. Chrome is now like an absolute last resort.
I convinced a vendor they needed to stop being Chrome-only. The sales guy was sitting next to me, I loaded the page in FF, and turned to him and said, "Seriously, you want us to install a browser we otherwise refuse to use for this?"
It was fixed that week. Unfortunately, this trick does not work very well on non-enterprisey sites or after you cut them a check.
