I've seen this several times in the past few days, running Firefox on Valgrind. I can't reproduce it consistently. It happens sometimes when a popup is shown and (I _think_) the popup moves to a different location immediately after it first appears. Can anyone suggest some mochitests to run, that test popups?
Popup tests are toolkit/content/tests/chrome/test_popup* (and test_panel*) Is there more detail about what value is uninitialized?
(In reply to Neil Deakin from comment #2) > Is there more detail about what value is uninitialized? It is nsMenuPopupFrame::mAlignmentOffset. This is a primitive type (nscoord, == int32_t or float) and nsMenuPopupFrame::nsMenuPopupFrame(nsStyleContext*) doesn't give it an initial value.
Comment on attachment 8908985 [details] [diff] [review] bug1400341-nsMenuPopupFrame-1.diff OK. This could probably happen when a menulist is used. Tests for these are toolkit/content/tests/chrome/test_menulist*
Pushed by firstname.lastname@example.org: https://hg.mozilla.org/integration/mozilla-inbound/rev/cfe02dcfa163 Uninitialised value use in nsMenuPopupFrame::SetPopupPosition(nsIFrame*, bool, bool, bool). r=enndeakin.