Yes, you can configure Thunderbird to open clicked links in Firefox while keeping Edge as the default browser. Here's how you can do it:
1. Open Thunderbird and go to the "Options" menu. On Windows, you can find it under the "Tools" menu. On macOS, it is located under the "Thunderbird" menu.
2. In the Options menu, select "Preferences" (on macOS, it is called "Preferences" directly).
3. In the Preferences window, click on the "Advanced" tab.
4. Under the "General" tab, click on the "Config Editor" button.
5. A warning message will appear. Click on the "I'll be careful, I promise!" button.
6. In the "about:config" window, you will see a search bar. Type "network.protocol-handler.warn-external.http" (without quotes) in the search bar.
7. Double-click on the "network.protocol-handler.warn-external.http" preference to change its value to "true".
8. Next, search for "network.protocol-handler.external.http" (without quotes) in the search bar.
9. Double-click on the "network.protocol-handler.external.http" preference and enter the path to your Firefox executable. For example, on Windows, the path might be "C:\Program Files\Mozilla Firefox\firefox.exe". On macOS, it might be "/Applications/Firefox.app/Contents/MacOS/firefox".
10. Repeat steps 8 and 9 for the preferences "network.protocol-handler.warn-external.https" and "network.protocol-handler.external.https" to handle HTTPS links.
11. Close the "about:config" window and the Preferences window.
Now, when you click on a URL link in Thunderbird, it should open in Firefox instead of Edge.