It looks like the issue is a change in the type Firefox reports for a certain element that I'm testing for a fix that I used to get the maps working in FF 2. The statement:
if(typeof(Element) == 'function'
returned true in Firefox 2.x, but in Firefox 3.x the return value from the typeof call is 'object' rather than 'function' (IE returns 'object' too, so at least this means they're now consistent. So I did a little searching on Live Search, and found the following solution from Dean Edwards, which tests for support for conditional compilation to determine if the current browser is IE:
var isMSIE = /*@cc_on!@*/false;
Then I just test the value of isMSIE, and either apply the fix or not, depending on the value.