This article explains how to change the default browser that Thunderbird uses to open URLs. These instructions apply to Thunderbird 91.10, so update to the latest version before you begin.

Thunderbird will usually pass the event to your default web browser. Normally, this will all go smoothly. However, if something goes wrong, you will need to know how to tell Thunderbird exactly which web browser you want to use.

Select Menu (the three lines) > Preferences.

Scroll down in the Preferences window and select Configuration Editor.