FireBug question

[Papa Bear]

Hello

I have started using FireBug for debugging a new web application.
I've just been doing a script level application for a few months
although I have a good many years experience with 3GLs.

Question: when I have my web page loaded and FireBug turned on, I
will often want to inspect the code and the hierarchy of <div>s
checking styles, layouts, etc. Most often I just click on the FireBug
icon on the far right of the status line and then click on HTML on the
FireBug menu and I'm off.

But occasionally, when I open the FireBug widow, the "Inspect" link is
dimmed out and clicking on HTML yields nothing.

I'm sure there's something I'm doing or not doing but I can't fathom
what it is.

Thanks in advance for your help.