local file

I recently upgraded to FF 1.5. My problem is I can't get it to read an 
html file passed to it from another application. For instance, in 
Dreamweaver, I've got FF identified as my primary browser. When I want 
to view the page I've just created I hit F12 and the page I'm working on 
is supposed to open in a tab within FF. Instead, FF opens a new window 
with the default webpage instead of the file I was expecting.

In another case, an applications' help files are HTML. Hitting the 
"Help" key results in FF loading a new window with the default/home page 
instead of the help file I was expecting.

So, can anyone tell me how to fix this?

Thanx!

Dale