macOS – How to Change Default Browser

look at: ~/.local/share/applications/mimeapps.list

if the file is not there, create an empty one, then use the chrome feature to set it itself as default browser. If this not work, try adding this content. (check for the right .desktop file for Google Chrome)

[Added Associations]
x-scheme-handler/http=chromium-browser.desktop

[Default Applications]
x-scheme-handler/http=chromium-browser.desktop

Thunderbird (at least version 6 here) appears to be using the XDG MIME actions specification. The preferences are stored in ~/.local/share/applications/mimeapps.list, and all desktop environments are supposed to respect them.

[Default Applications]
text/html=chromium.desktop
x-scheme-handler/http=chromium.desktop

Older versions of Thunderbird may still be using GNOME's Gvfs for this. You can check using gconftool-2:

$ gconftool-2 --get /desktop/gnome/url-handlers/http/command
firefox %s

If that's the case, the best option is to configure Gvfs to use xdg-open for all URL schemes, which in turn should invoke the right program from mimeapps.list:

$ for scheme in http https about unknown; do
    gconftool-2 --set /desktop/gnome/url-handlers/$scheme/command \
        --type string "xdg-open %s"
done

Or you could try xdg-settings, which... honestly, I'm not sure what it does:

$ xdg-settings set default-web-browser chromium.desktop