A recurring bug with a black box covering text input field

I have a repeating problem where LanguageTool starts covering the text input field with a black box that prevents me from seeing the text (Firefox browser). When I remove the extension, the problem disappears, I can then reinstall the extension, it works for some time and then randomly in the future the dreaded black box of doom reappears.

This is how it looks:

Hi @LeslieFH ,

Thank you for bringing this issue to our attention - we’re sorry to hear about the mysterious black box!

We’ve escalated this matter internally and will ensure to keep this post updated as soon as we have more information to share.

Kind regards,
Eline

Hi @LeslieFH, thanks for reporting. I’m one of the developers behind the browser extension and would like to further investigate. Which website is this problem happening with? It looks a bit like Facebook?

This is Facebook, but it occurs on any text input field, for example on Discourse when I’m writing a comment.

(Right now the extension is working properly :-)).

Thanks. Which other extensions do you have installed? There might be a conflict with LT’s Firefox add-on