I upgraded most packages to unstable, which somehow seems to have fixed it.
- Bug#910433: thunderbird: Open hyperlink and attachments ... Johannes Rohr
- Bug#910433: thunderbird: Open hyperlink and attachm... Carsten Schoenert
- Bug#910433: thunderbird: Open hyperlink and att... Johannes Rohr
- Bug#910433: thunderbird: Open hyperlink and... Johannes Rohr
- Bug#910433: thunderbird: Open hyperlink... Johannes Rohr
- Bug#910433: thunderbird: Open hype... Carsten Schoenert
- Bug#910433: thunderbird: Open ... Johannes Rohr
- Bug#910433: thunderbird: O... Johannes Rohr