I recently discovered the solution to this problem. I had a script that worked great in all browsers, no errors. Then, when I was upgrading it suddenly in Firefox I was getting the "Error in parsing value for property 'xxx'. Declaration dropped.url... (line 0)"
I compared the two side by side and discovered the <!DOCTYPE> declaration was the culprit.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> worked fine, but when I tried to upgrade to XHTML and use
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> the problem popped up.
Like the poster, I was using very simple, standard code and the problem showed up with various types of CSS properties. In my case, is was reassigning the top and left properties for a <span> style to move a graphic around the screen with the mouse.
<span id="cursorDiv" class="cursorstyle">
<img src="images/something.gif" id="cursor" class="cursorstyle" alt="">
spanObj = document.getElementById("cursorDiv");
spanObj.top = 100;
spanObj.left = 100;
The spanObj.top = 100; and spanObj.left = 100; lines were giving me a problem with XHTML, but not HTML. Anyone have any idea why? Seems like pretty standard stuff to me, is it somehow violating the DOM or some other aspect of CSS?