I have a resizable dialog, which I can resize so small that none of
the buttons are seen anymore. I don't like that very much and wanted
to change that so I used minheight. However it had no effect.

I googled a bit, but either I used the wrong keywords ("resizable",
"minheight") or no one else is bothered by it.
The window and dialogs in Thunderbird and in the addons I use in there
show the same behaviour (i.e. resizing is not stopped when the dialog/
window gets too small). So I just can't look into someone else's code

So any hints or addons with this behaviour would be appreciated.