Firefox and Thunderbird are obviously meant to be used together, but an annoying detail is that under Linux they are still not setup that way. Firefox is not configured to launch Thunderbird to handle email links, nor is Tunderbird configured to delegate web links to Firefox. I review below how to setup both software.
user_pref("network.protocol-handler.app.http","/usr/local/firefox/firefox"); user_pref("network.protocol-handler.app.https","/usr/local/firefox/firefox");changing the values in italics by the actual values in your system. Changes will be effective next time your start Firefox.
network.protocol-handler.app.mailtoSet the value to Thunderbird binary file path, e.g. /usr/local/thunderbird/thunderbird