Hi there,
I have some projects where the browser is visible in PRV but most other projects it's not.
When it is visible in PRV "B" will toggle it's visibility in PRV, and also in track view.
If I leave it open in one it will be open in the other.

In projects where it's not initially visible in PRV, "B" will not make it visible.

Can someone point me to where this is option/behavior controlled?

Thanks!

Can't help you with understanding it, but I've observed the same thing. 
 
Try this:  float a PRV window.   Press B (the browser will, maybe appear or disappear).   Press B again (maybe it works)  Press B again: nothing happens.   Now minimize the PRV window, and then bring it back to focus.  Press B: it works again, once or twice, then stops working.    

I always thought it was because I had a B shortcut for "bounce to tracks' in Track view, but maybe there's a more general problem.

Ahhh ... if I float it and close it in PRV ... then in track view make it return I think this will fix it.
Fix meaning I don't want it in PRV.
Thanks