The proper solution is to prefer `start` (Windows), `open` (OSX), or `xdg-open` (everything else... usually but not always present) when present instead of calling the browser directly.

That way, you're using the same "delegate to the desktop's associations system and let the user's preferences control new window vs. new tab" behaviour on all OSes where it's reliably possible.

(Yes, it would guarantee that all open* functions are equivalent, but that's already the norm in a lot of cases... especially with Firefox where one of the guiding design principles is ensuring that the user retains control of their browsing experience.)