Shifting focus to a browser tab

[jhsachs]

Here's a small JavaScript puzzle, probably trivial to those more familiar with JavaScript than I am.

 

My PHP script wants to open a new browser tab, display a page in it, and shift the focus to it. If the tab is already open, it wants to shift the focus to the tab without opening a new one.

 

I found that window.open does what I want, as far as opening the tab goes, out of the box. Thus I can open the tab if and only if it doesn't already exist like this:

 

window.open('www.somewhere.com/newtab_page.html', '_newtab');

 

window.open returns a reference to the tab whether it already exists or not, right? So I should be able to open the tab if it doesn't exist and make it the current tab like this:

 

var newtab = window.open('www.somewhere.com/newtab_page.html', '_newtab');
newtab.focus();

 

But it works only if the tab does not already exist. If the tab exists, it does nothing. Why is that, and how can I fix it?

[jhsachs]

Just in case this is a platform-dependent issue, I'm using Firefox 4.0 under Windows XP.