I'd believe that you use the same password... I myself has quite a few, and I use the same password for all of them.
If you are using the same password, you should be able to switch from account to account easily. What I do is to go up the my name, well the part where it says, "Hello, Pizzicato" and beside it is a drop down thingy. There I can choose which subaccount I want to go to. Just note, if your name is too long, you won't be able to see the dropdown thing. XD
I don't know about the bookmarks really, but -
EDIT: just tried it out, and no, it does not get added to your main account folder. ^.^
I hope I helped!