Glad it worked well in Firefox!
Normally, I add Windows/Linux/Mac executables as downloadables for my PICO-8 games, but I see that for some reason I didn't do this for Dank Tomb. I'll make a note of adding those - once they're up, you can play without PICO-8 just by using the standalone executables. I'll try to put up the executables some time next week, since there is really no reason for them to not be here.
If you want to play the original cartridge file, you do need PICO-8 to load it.