So why firefox directs to the default browser when I enter an ip address with port e.g. 123.45.6.789::8888 in the address bar?? Just to be clear, I was trying to access jupyter lab instance of another computer. This feature is greatly appreciated. Well, to be fair, I am not at all up-to-date with networking security stuff and sorts, but seriously?

Anyway, fix for firefox (version 72.0.1): go to about:config (yes, let’s live dangerously) and set the keyword.enabled to false (by double-clicking it).

Sources