Trapped focus in iframe using Dialog with Firefox

[aschojz]

I'm using the Dialog-Component to display an embedded iframe-preview of a calendar, along with some input-fields to make some changes. Now in Firefox the focus is trapped inside the iframe and I can't write anything in my inputfields. The inputs and buttons do have hover-state and are clickable, but focus and input is not possible. Chrome and Safari don't have the problem.

Any suggestions or ideas how to fix that?