STEPS TO REPRODUCE: 0. Have a local debug build. 1. mkdir emptydir && ./dist/bin/firefox -profile emptydir -no-remote --> "default browser" dialog appears ACTUAL RESULTS: Two instances of this assertion: { ###!!! ASSERTION: Uh, inner window set as event target!: '!win || !win->IsInnerWindow()', file ../../../../mozilla/content/events/src/nsDOMEvent.cpp, line 878 } One instance happens when the dialog appears, and the second happens when I dismiss the dialog. From intercepting the assertions & looking up the stack, these assertions trace back to firing "DOMWillOpenModalDialog" and "DOMModalDialogClosed" events, from here: > 51 nsAutoWindowStateHelper::nsAutoWindowStateHelper(nsIDOMWindow *aWindow) > 52 : mWindow(aWindow), > 53 mDefaultEnabled(DispatchCustomEvent("DOMWillOpenModalDialog")) > 54 { http://mxr.mozilla.org/mozilla-central/source/embedding/components/windowwatcher/src/nsAutoWindowStateHelper.cpp#51 and here: > 62 nsAutoWindowStateHelper::~nsAutoWindowStateHelper() > 63 { [...] > 71 DispatchCustomEvent("DOMModalDialogClosed"); http://mxr.mozilla.org/mozilla-central/source/embedding/components/windowwatcher/src/nsAutoWindowStateHelper.cpp#62

Adding dependency on bug 393707, which added the lines of code quoted in comment 0. (Not sure if the assertion-failure traces back that far -- hence, I'm marking this as "depends on" that bug, rather than "blocking" that bug.)

This is a dup of a bug which bz fixed yesterday or so... Not sure if the patch landed yet.

Oh, awesome. Sorry for filing the dupe -- I just relied on the new-bug-form's dupe suggestions (and that didn't turn up any actual matches), rather than doing an actual bug-search. Duping.