Grid overlay toggle

[Melisa]

I recently downloaded Firefox and Firebug on my Mac.  I have been using the grid overlay toggle and it has been working in a way that surprises me; although it may be normal.  

Specifically, when I first open Firebug I am able to toggle the grid overlay on.  However, if I toggle it off or if I reload the page then I am not able to toggle the grid overlay on.  I need to close Firebug and reopen it before I can activate the grid overlay toggle.  Is this normal behavior?  If so, that's fine.  If not, could someone please help me figure out what is causing this behavior?

Take care,

Melisa