not on Windows, so I need someone with the Steam version to test this for me
Go to the browser, press F12, and paste this in:
$("#joinTrigger").attr("src", "steam://rungameid/250340//-connect 104.237.141.93:40000");, and press Enter.
This should launch Blockland via Steam, and connect you to Boss Battles. If this works, I'll go ahead and add an option that will switch between the blockland:// and steam:// protocols. v20 master servers will be forced to blockland20:// once/if I figure all that out.
It works. Firefox pops up with a prompt to open with steam, and then steam makes a message confirming you want to run the game with those arguments.
edit: missed the replies already on this page apparently.