I just installed Ubuntu 24.04 (yeah... it's already 2025...) and started to setup my new system. Tons of software to re-install, etc.

I use Firefox as my default browser, but I also have Chrome and Opera for all sorts of reasons (Chrome plays more videos and Opera allows me to be logged in as a different user in a few systems).

Today I clicked on a link in Thunderbird, which I've been doing a lot. Only, it opened the Chrome browser instead of Firefox. I was really surprised since that usually works as expected.

I went to my System Preferences, Apps, Default Apps... and sure enough, it says Firefox is the default. What gives?! Well, I do not know what really happens in this case, but even though the default shows up as Firefox, under the hood, the system is confused, somehow. I changed the default to Chrome and then back to Firefox, and tried the same link in Thunderbird. Bing! It opened in Firefox.

So that's was it. Reseting the default app. fixed the issue for me. Simple enough. Although first I searched the Thunderbird settings for a way to select the browser it would use and could not find it. Before, it had http and https entries in the list of media and how to open them, but those entries are gone.

Here is a screenshot of where the settings used to be:

Here is a screenshot of the Default Apps in your system settings: