STR: 1. Open the following URL: http://board.byuu.org/viewtopic.php?p=64035#p64035 2. Scroll all the way down 3. Start autoscrolling and try to scroll downwards 4. Try moving the mouse pointer around for a bit (but keep it below where you started autoscrolling, as if you're still trying to make the page go down more) 5. Alternatively enter Full Screen and watch how the page elements behave In certain spots some of the page elements continuously start twitching up and down. I have attached screenshots showcasing the behavior. Observed on lastest Nightly on Windows XP and Windows 7 64-bit.

Regression window(m-c) Cannot reproduce: http://hg.mozilla.org/mozilla-central/rev/6fe7dd2f8f57 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/15.0 Firefox/15.0a1 ID:20120510021321 Reproduce: http://hg.mozilla.org/mozilla-central/rev/b7b6565d12a0 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/15.0 Firefox/15.0a1 ID:20120510050721 Pushlog; http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=6fe7dd2f8f57&tochange=b7b6565d12a0 Regression window(m-i Cannot reproduce: http://hg.mozilla.org/integration/mozilla-inbound/rev/b5304fd23df9 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/15.0 Firefox/15.0a1 ID:20120509222721 Reproduce: http://hg.mozilla.org/integration/mozilla-inbound/rev/67091352b7d2 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/15.0 Firefox/15.0a1 ID:20120509223521 Pushlog; http://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=b5304fd23df9&tochange=67091352b7d2 Triggered by:Bug 681192

I can also reproduce on Linux http://hg.mozilla.org/mozilla-central/rev/22a58090fa70 Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/15 Firefox/15.0a1 ID:20120512030520

screen capture http://youtu.be/YFSD3n3bYvk

Last good: c3d3bfb3b68d First bad: 9d9a3edaa0b9

Comment on attachment 623639 [details] [diff] [review] better patch >layout/generic/nsIScrollableFrame.h >+ virtual void ScrollToCSSPixels(nsIntPoint aScrollPosition) = 0; Please add to the doc comment that the scroll mode is INSTANT. Shouldn't nsScrollBoxObject::ScrollTo change in same way?

Yes, I'll do that separately.

Comment on attachment 623885 [details] [diff] [review] nsScrollBoxObject fix r=mats

Fx 15.0a1 2012-05-19 I can still reproduce parts of this, although it is fixed for autoscrolling. Using the same URL, or one of quite a few others (http://www.less-broken.com/blog/2012/05/no-www-considered-harmful.html is one example), I can reproduce twitchy elements using the following steps: 1. Scroll to the bottom of the page with the mouse wheel. 2. Scroll down some more with the mouse wheel. (Alternative to step 2 is scroll left with a tilt-wheel, if you have one). This doesn't happen every time, but fairly often. (I have no idea why the blocker got removed, thanks Ryan).

bmo issues

Confirmed with STR(Alternative to step 2 is scroll left) of comment #17 in http://hg.mozilla.org/mozilla-central/rev/642d1a36702f Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/15.0 Firefox/15.0a1 ID:20120519030527