After doing a full install of Fedora 39, I had to reinstall Thunderbird and whatever I may have once set up to forward links to my browser has broken.
Very likely if I was using Firefox this would "just work". Thunderbird claims to use my default browser (whatever it is), but that simply doesn't work. Exactly how to specify it (in a way that thunderbird will understand) when using linux along with XFCE is unknown to me.
Scroll to the bottom of Settings/General and there is a button to launch the config editor. Search for "warn-external" and change the settings for http and https to true. The "Files and Attachments" section will not include http or https unless you do this.
Go back to Settings/General and scroll down to "Files and Attachments" and you should now see entries in the menu for http and https. The game now is to fool with the "Action" for each of these. Telling it to use the default browser does not work. You can select "Use other" and that will bring up a file browser allowing you to specify whatever you might like. I set "/bin/google-chrome".
I do this for three types of files and attachments:
Adventures in Computing / tom@mmto.org