Ah yes, JavaScript, my specialty!
Well first, I don't know how you script works without semicolons at the end. I didn't realise you could do that with JavaScript, but it seems to work to an extent without the semicolons. I think you at least need to add semicolons into your disableMenu and enableMenu functions, they might be causing the code to not be able to display your previous menu link.
Maybe try adding a line before this line:
CODE
comic.src = "Comics/Jim"+CurrComic+".GIF";
So it says this:
CODE
var comic = document.getElementById("comic");
comic.src = "Comics/Jim"+CurrComic+".GIF";
And for that to work you'd need to change this line:
CODE
<img name="comic" src="Comics/Jim1.GIF"><br />
Into this:
CODE
<img id="comic" src="Comics/Jim1.GIF"><br />
QUOTE
My brother says that part of the reasons is because "FireFox is render once"
He's right yeah, but I'm not sure if that really applies to your problem. I did run into that problem though when coding the part of StarCraft.org that collapses the navbar, so it is there.