[clug] Thunderbird opening links in chrome, but I want to use Firefox

[Tony Lewis]

Hi all,

I upgraded to Kubuntu 24.04 recently, and now Thunderbird will launch 
links with Chrome.  I've had it using Firefox for years.

Going to 24.04 forced me into using the Snap version of Thunderbird, 
which gave me some teething issues but now seems OK. In fact for a while 
it wouldn't open links, to do with apparmor. I was getting errors like:

     apparmor="DENIED" operation="userns_create" class="namespace" 
info="User namespace creation restricted" error=-13 profile="unconfined" 
pid=58873 comm="chrome" requested="userns_create" denied="userns_create"

Which certainly indicates Thunderbird is trying to launch Chrome.  Now I 
don't get the error, I get Chrome, but I want it to Firefox.

My default handler in the desktop is set to Firefox.  I confirmed this 
with `xdg-open google.com`, and I even switched to Chrome temporarily, 
tested it, and switched back.

I can't see any suitable settings to change, and I can't seem to find 
anything in the advanced settings either.  Searching the internet didn't 
seem to help me either.

Any clues?  Thanks in advance,

Tony