Arch Linux set default browser

open terminal and execute following commands

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

replace browser with chromium or firefox

example

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

or

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