First, IE is the only surefire way to support SharePoint. All others try but
they fall short in some category or another. (Not that I am a fan of IE by any
stretch; I'm a Chrome junkie.)

Second, try using jQuery instead. It's supposed to be more browser-agnostic than
straight JavaScript.

jQuery is an idea. But really, shouldn't javascript work the same in any
browser? Its just javascript running queries on html code...

Javascript runs based on an external library provided by the browser. Each
browser has their own flavor of javascript library, just like html and css.
JQuery is better, but each browser will be somewhat different there also.

I figured something out. replace innerHTML does not work in Netscape
browsers for sharepoint. Instead, you must work by childnodes.

This works in IE but not in Firefox:
document.getElementById(idName).innerHTML =
document.getElementById(idName).innerHTML.replace(oldstring, newstring);
This works in both browsers:
document.getElementById(idName).childNodes[1].nodeValue =
document.getElementById(idName).childNodes[1].nodeValue.replace(oldstring,
newstring);

Yes, jQuery is just JavaScript, *but* it is JavaScript that has been honed
and refined to take into account all sorts of browser inconsistencies.

However, in this case, I'd bet that Firefox is getting different element IDs
from the server -- unless of course your code below is copied/pasted, in
which case you appear to have a typo :)

yes, I noticed the typo; no, it was actually my own typoed code... I
figured it out however. I had to select the items by nodes in certain cases to
work in firefox.