TYPO3 Core

Help from http://www.mozilla.org/docs/dom/domref/dom_window_ref76.html for whoever knows where the parameters for the window.open-function are gathered:

The solution would be to expand the paramter of the window.open-function with the string: 'directories=1'. (no official javascript, but a valid option for the gecko-engine)

everyone can use this as a workaround:
"Mozilla and Firefox users can force new windows to always render the
Personal Toolbar/Bookmarks toolbar by setting
dom.disable_window_open_feature.directories to true in about:config or in
their user.js file."

I'm sorry but this does not seem to be possible:

I tested "directories=1" with Firefox 1.04. It works fine and makes the window look the same way like a window looks if it is openend using the target="_blank" paramenter.

However, it is not possible to open a sidebar inside (e.g. the bookmarks tab, etc.) which is what I wanted to achieve.

So unfortunately this is not possible. What I will change is to add te directories=1 parameter depending that it doesn't break anything in other browsers...

Fixed in 4.0. Actually the solution was very very easy :-)
Many thanks to Martin Kutschker for giving me this great hint.