A small change from firefox20 to firefox21

<Div style = "width: 500px; position: relative; Border: 1px solid black;" onclick = "alert ([This. scrollheight, this. offsetheight]);">
<Div style = "float: Left; width: 200px; Height: 200px; Border: 3px">
Click me
</Div>
</Div>

Firefox20-: 0, 2

Firefox21 +: 200,2

Other browsers:

Firefox, from 20 to 21, was originally modified with a bug that is inconsistent with others. However, the negative error caused a bug on one of my pages... I will not remember this error in this article. I will see if I can figure out under what circumstances this error may occur in a few months.