I’m writing this down here so I don’t forget it.
I had an issue on my Ubuntu Linux box where when I right-clicked on a link in the terminal it would open in Firefox, even though my default browser is Chrome. Clicking on links in GUI applications worked just fine (they opened in Chrome); it was just links I tried to open from inside the terminal that would insist on opening in Firefox.
Normally this sort of thing would be fixed using the update-alternatives command, but not so in this case.
Here are the commands which fixed it:
xdg-mime default google-chrome.desktop x-scheme-handler/http
xdg-mime default google-chrome.desktop x-scheme-handler/https