Hi,
just to let you know, I was able to solve this mystery.
Since the DFFS came with a solution I had to wait until the reseller did the update… which didn’t solve anything.
But I found there was another piece of javascript on this form (in a CEWP) which did refer (and load) a different jquery version. After removing this reference, the tabs in the background appeared again, and everything worked fine.
Best regards,
Nicole