Why not have the list down the left of all quests you are on split into "Main", "Side" and "Leve" sections.

They could be further split down by zone too which would be useful.

Then, have a pane on the right side of that window to show the quest details in when you select one.

You know... how WoW now does it

It means that...

A) You don't have to wait for it to open another window and then have to close that window before viewing another one.. you can just click down the list... much more intuitive.

B) Removes the UI lag-time from opening new windows as the quest details could all be loaded when the journal is opened (this data should really be cached client side too) so it is instant when clicking on each quest.