Launching Windows Firefox from WSL works, just set the BROWSER environment variable

Pontifications

I was wrong when I wrote: Still can’t launch Firefox from Windows Subystem From Linux without a Selenium server and some hacks that nobody has working (Chrome works though) back on September 9, 2018.
It’s easy to use the Launchy ruby gem
Just set the BROWSER enviroment variable and the Launchy just works:

export BROWSER='/mnt/c/Program\ Files/Mozilla\ Firefox/firefox.exe'