Locking applications to a particular workspace?

[Kevin Martin]

Is there any way to lock an application to a particular workspace (like
with fluxbox)?  For example, I setup four workspaces.  On workspace two
I run thunderbird and on ws3 I run firefox.  When I click a link in an
email in thunderbird it's setup to open a new tab in firefox for the
webpage.  However, firefox then takes focus and jumps to workspace two. 
I want it to stay on ws3 and I'll look at the webpage there.  Is there
some way to make this happen?  That's one of the reasons I was using
fluxbox is it's ability to do just that.  I figure if fluxbox can do it
then maybe it's just something I'm missing in xfce.

Thanks.

Kevin