Not working with BetterBird

[lenusch]

Describe the bug
Addon is not working for "Betterbird" (https://www.betterbird.eu/)

Reproduction steps
Just have a Look at Spam E-Mails, Score is not working at all, even with correct headers.

[mburr]

I believe this is fixed in v1.5.0 by #59

For me, Spam-Scores v1.5.0 is working in BetterBird 128.7.0esr-bb22 (64-bit) on Win11 v10.0.26100.6899