I use Ubuntu 18.04 with KDE. My default PDF viewer is Okular and it has worked as intended (when I open PDF, it laucnhes Okular).

That has changed recently: If I now open PDF i.e. from Dolphin, Okular app opens just normally. However, the default app for Firefox and Thunderbind seem to have suddenly changed to Evince. No configuration has been touched.

Any idea why FF and TB now use different app as default? I tried even removing Evince, but then FF and TB opened PDF with Inkscape.

My own suspect is that this is some new bug that come with some recent upgrade.

Any ideas? Thanks!

  • You can set the default viewer for pdf attachments in Thunderbird in the preferences under "Attachments → Incoming". It was “Always ask” for me, but it never asked. After choosing an application, it respected my choice. – Scz Mar 27 '20 at 13:54

I see the same behaviour (Manjaro 19.0.2, KDE 5.68.0 / Qt 5.14.1): Thunderbird 68.6.0 64-bit is configured to use "system default" for display of PDF attachments. In KDE file associations, the PDF viewers are (in this order): 1. okular 2. LibreOffice Draw 3. Inkscape

Double clicking the PDF attachment of an email opens it with... yeah! - Inkscape grr

Now, choosing a certain application as PDF handler within Thunderbird does what you'd expect. So that could be a workaround, but of course I don't want to accepts this crumpy behaviour as a solution.

When I change KDE's file associations by rotating the viewer order and put LibreOffice Draw in the first place, it does indeed work - PDF is opened with LibO Draw!

Next, I put Okular back on the top of the list - and astonishingly now Thunderbird does what one would expect...

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