Since I migrated to Xfce it seems thunderbird does not uses the default browser setting nor the /etc/alternatives/x-www-browser. The solution to change the default browser to chrome for example is to go to Preferences/Advanced/Config editor and change the network.protocol-handler.warn-external.http to true. This way next time you will open a link you will be prompted to select a browser and you can choose to remember the setting.
Comments:
ghantoos -
Thanks for the share!
Grant -
Thanks for this.