Sebastian G.

Alright, I may found what caused this to happen. It's another add-on called RequestPolicy. It blocks resources from cross-sites being requested unless the source is allowed to request everything or...

Well, I created a ticket (see their #377) and maybe it's reasonable and it will be added to the allowed sources or not. Maybe there'll be help from other people....

According to https://developer.mozilla.org/en-US/docs/Extensions/Thunderbird/Building_a_Thunderbird_extension_3:_install_manifest the em:id for Thunderbird is ////{3550f703-e582-4d05-9a08-453d09bdfdc6}////

Patching the .rdf file is not an option here either. Installing works, but there's the same(?, at least similar) error as for #7 I'll be available for testing and since...