I don't know if this answers your question, but there are 2 ways to get to where you want to post a new thread and I guess the answer is you have to leave the current thread you are in. If I'm wrong, someone will correct me soon.
Go to the top left of the blue bar and click SMF. This turns into forums and then you scroll down to find the subject you want to post in.
The other ways is at the bottom of the page of the post you are reading on the right you just scroll to the subject you want and it will "jump you there.
I use Firefox, and if I don't really want to leave the area I'm in, I just right click and open in a new tab.
Did this help?