Grammar and Spell Checker — LanguageTool

Yettwasezmel 2 ɣef 5 n yetran

sɛur Guido3 di Jan. 20, 2023 · aseɣwen yezgan

Does work well in Firefox but not in Thunderbird. Extension is installed. I see a LanguageTool-Button in every E-Mail window next to the Attachments-Button, where I can access the Settings for LanguageTool. But it does not mark any errors in the text, does nothing

Thunderbird 102.7.0 on Windows 10
LanguageTool 6.0.5

@Christopher Blum: I've tried that already. I have just one other add-on (Provider for Google Calendar) and deactivation does not solve the problem. You can find a screenshot here:
postimg.cc/2bzPDTDw