Yup, that did the trick.

Unfortunately only three tabs can be open at the same time on a 1920x1200 screen.

Perhaps it is possible to shrink the panels a bit, or lock them open (even if the lowest one then can slide out of screen, but then I can chose myself which other panel I would close to the the lowest one back in view again, aso). Now it just forcefully closes the lowest tab.

Edit: I tried also the jf-script in the *first link*, but that one allows only one of the two lowest panes to be open at the same time, either Construct or transform, so that one doesn't make any difference really.

// RIL