Filters correctly floating on the right side of the screen (Firefox)

When using filters, the layout of the 'models' screen is broken in Firefox.
The .span3 containing the filters receives padding because of the .well class.
As the box-sizing model is apparently different from Chrome's (don't ask...), this padding gets added to the fixed width of the element in Firefox whereas is included in the width in Chrome.
I moved the .well to a child of the .span3 container and the layout works fine under Chrome and FF now.