My default browser is set to Firefox but links open with Chromium

I'm going to guess the following

• all of those tools use XdgUtils
• if you type xdg-open http://google.com it'll open with Chromium
• and that you have the problem described in this Ubuntu forumspost

So my suggested answer is:

$ xdg-mime default firefox.desktop x-scheme-handler/http

(and ditto for https)

I needed to add this:

sudo update-alternatives --config x-www-browser

And choose Firefox as default browser. Only after that it was working. The change:

xdg-mime default Firefox.desktop x-scheme-handler/http

didn't work itself. After adding both — it is working just fine.

gvfs-mime --set x-scheme-handler/http <whatever chrome is>.desktop
gvfs-mime --set x-scheme-handler/https <whatever chrome is>.desktop