The only thing that looks a bit like what I'm trying to achieve is this, but this works only for IE... for firefox I found that information, so is it not possible to open tabs, just new windows?
And the attach method is accessing only already OPEN tabs/windows... Is there a way to decide to open a specific link in a new window/tab? I searched in the documentation, but I didn't find such a function...
Ok thats not a solution but a work-around:
I switch to ruby mechanize, is quite different to use, but allows to do multithreading and everything without a visible browser window...