Thunderbird keeps setting itself as default browser, causing local html files
to be opened as attachment to a new email message, and links to be
opened no-where.

I'm using Gnome as my desktop environment, and want to have Firefox be
its default browser.

Thunderbird is not a browser so shouldn't even try to make itself the
default.

Hello Matijs,

Am 17.05.2018 um 15:42 schrieb Matijs van Zuijlen:

Thunderbird itself is using the settings
'network.protocol-handler.app.http(s)' for referencing the to be used
browser if one of http protocols is called.

The default is set to 'x-www-browser' (see
/etc/thunderbird/pref/thunderbird.js) which is linked to another link
handled by update-alternates.

These settings shown above are the default case for a long time, so if
Thunderbird tries to open Thunderbird for html links you have some non
default settings.

The settings for network.protocol-handler.app.http(s) can be modified
within your preferences so first have a look into your profile and check
if there is something changed.

Another possibility to look at is the file
$HOME/.thunderbird/[your_profile]/mimeTypes.rdf

Here also some different browser can be declared. Look for something
like this especially on 'NC:path':

You can safely remove such a entry.

Hi Carsten,

Your detailed response sent be on a cleanup of all settings related to this.

Yes, /etc/thunderbird/pref/thunderbird.js contains the correct value.

For me, this alternative is set to /usr/bin/epiphany-browser.

I can't find it in prefs.js in my profile. However, if I go to the
Preferences window in Thunderbird, under Attachments/Incoming there are
settings for http and https. These are currently set to 'Use firefox',
but their defaults are 'Use Thunderbird'. There is also an entry for
HTML Document, currently set to 'Always ask'. Its other options are 'Use
Thunderbird (default)', and 'Use gvim'. No actual browser is listed there.

I'm guessing this is what is edited under Attachments/Incoming? I'm
still surprised by the defaults presented. Oddly, for PNG Image, the
default is Firefox.

In addition to checking the above, I have also cleaned up the settings
for my Gnome desktop environment. There were a lot of old .desktop files
lying around, some indeed setting thunderbird or icedove as a potential
browser. As a result, in Gnome's Settings application under Default
Applications, the Web option finally no longer listed Thunderbird as an
option, and had Firefox set as its value. All seemed well.

However, this morning I noticed:

   $ xdg-settings get default-web-browser
   thunderbird.desktop

I immediately checked Gnome's settings, and it still listed Firefox.

Then just now, I ran:

   $ xdg-open https://www.matijs.net/

.. and it seems this tried to open Thunderbird, although I can only tell
from the AppArmor messages appearing, since nothing is actually shown.
In Gnome's settings, the Web entry now again shows Thunderbird.

I'm not sure what's going on here or where xdg-settings gets its
information.

Regards,
Matijs

Hello Matijs,

this you can easy check. ;)
Backup the file, change an entry and diff the files.

From your local config ~/.config/mimeapps.list.

https://wiki.debian.org/HOWTO/DefaultWebBrowser

xdg-open uses local configs is they are done and this is mostly the
case.

Change the default browser to what ever you like here and your problem
will go away I guess.

Regards
Carsten

this could be the same issue: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=948691