Created attachment 649963 [details]
Open the testcase, see horizontal scrollbar. We didn't use to have one. Might be Linux only.
The first bad revision is:
user: Markus Stange <email@example.com>
date: Fri Aug 03 12:35:14 2012 +0200
summary: Bug 770453 - [b2g] Semi-transparent scroll bars should not occupy content-flow space. r=roc
Created attachment 651535 [details] [diff] [review]
Looks like the argument was in the wrong spot accidentally, meaning we got the min size where it was intended for us to retrieve the pref size.
Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/17.0 Firefox/17.0
Verified with Ubuntu Unity and XFCE (with the help of lcamacho). Firefox 17 beta1