Firefox became unstable with 5.2, works fine with 5.1.2

Hi,

after upgrading from 5.1.2 to 5.2 on my PowerMac G4 (400MHz) I noticed some
stability problems.

Firefox 3.6.28, from pkgsrc-2012Q3, sometimes refused to start or locked up
during use. Also the right scroll bar could no longer be controlled with
the mouse wheel after some time (but clicking on it with left mouse button
still worked).

These problems, especially the one with the scroll bar, are similar to those
I experienced on my Pegasos 2 (ofppc) with NetBSD 6.0 and current. They
started around 5.99.52.

When I downgraded to 5.1.2 (downgrading userland alone was not sufficient!)
the problems were gone! I could no longer reproduce any of them, even after
several days of use.

So this might be the chance to locate the bug. Can anybody remember what had
been pulled up to 5.2, which is capable to cause these problems? Maybe it
is the same that had changed between 5.99.48 and 5.99.52?

-- 
Frank Wille