click on "mail to" - links causes double-mails

[cmyk61]

Hi all,

since a few months I realize a strange behavior firefox+thunderbird

When I click ONCe on a button "mail to" on any webpage, thunderbird opens TWO empty mails with the adress I wanted to send the mail to.

for example here: https://www.kaiser-natron.de/impressum/

My mouse works proper!

Bug or feature?

regards

Ralf

[siffemcon]

Maybe TB is listed twice in Default Apps?