Assertion failure: aActiveTime >= 0 (Expecting non-negative active time), at /src/dom/smil/nsSMILTimedElement.cpp:1988 #0 nsSMILTimedElement::ActiveTimeToSimpleTime(long, unsigned int&) /src/dom/smil/nsSMILTimedElement.cpp:1986:3 #1 nsSMILTimedElement::SampleFillValue() /src/dom/smil/nsSMILTimedElement.cpp:2204:5 #2 nsSMILTimedElement::DoSampleAt(long, bool) /src/dom/smil/nsSMILTimedElement.cpp:691:11 #3 nsSMILAnimationController::DoMilestoneSamples() /src/dom/smil/nsSMILAnimationController.cpp:581:30 #4 nsSMILAnimationController::DoSample(bool) /src/dom/smil/nsSMILAnimationController.cpp:342:3 #5 mozilla::PresShell::DoFlushPendingNotifications(mozilla::ChangesToFlush) /src/layout/base/PresShell.cpp:4176:46 #6 mozilla::PresShell::DoFlushPendingNotifications(mozilla::FlushType) /src/layout/base/PresShell.cpp:4058:3 #7 nsDocument::FlushPendingNotifications(mozilla::FlushType, mozilla::FlushTarget) /src/dom/base/nsDocument.cpp:8545:14 #8 nsDocLoader::DocLoaderIsEmpty(bool) /src/uriloader/base/nsDocLoader.cpp:703:14 #9 nsDocLoader::OnStopRequest(nsIRequest*, nsISupports*, nsresult) /src/uriloader/base/nsDocLoader.cpp:632:5 #10 non-virtual thunk to nsDocLoader::OnStopRequest(nsIRequest*, nsISupports*, nsresult) /src/uriloader/base/nsDocLoader.cpp:488:14 #11 mozilla::net::nsLoadGroup::RemoveRequest(nsIRequest*, nsISupports*, nsresult) /src/netwerk/base/nsLoadGroup.cpp:629:28 #12 nsDocument::DoUnblockOnload() /src/dom/base/nsDocument.cpp:9374:18 #13 nsDocument::UnblockOnload(bool) /src/dom/base/nsDocument.cpp:9296:9 #14 nsDocument::DispatchContentLoadedEvents() /src/dom/base/nsDocument.cpp:5688:3 #15 mozilla::detail::RunnableMethodImpl<nsDocument*, void (nsDocument::*)(), true, (mozilla::RunnableKind)0>::Run() /src/obj-firefox/dist/include/nsThreadUtils.h:1192:13 #16 nsThread::ProcessNextEvent(bool, bool*) /src/xpcom/threads/nsThread.cpp:1037:14 #17 NS_ProcessNextEvent(nsIThread*, bool) /src/xpcom/threads/nsThreadUtils.cpp:513:10 #18 mozilla::ipc::MessagePump::Run(base::MessagePump::Delegate*) /src/ipc/glue/MessagePump.cpp:97:21 #19 MessageLoop::RunInternal() /src/ipc/chromium/src/base/message_loop.cc:326:10 #20 MessageLoop::Run() /src/ipc/chromium/src/base/message_loop.cc:299:3 #21 nsBaseAppShell::Run() /src/widget/nsBaseAppShell.cpp:158:27 #22 nsAppStartup::Run() /src/toolkit/components/startup/nsAppStartup.cpp:288:30 #23 XREMain::XRE_mainRun() /src/toolkit/xre/nsAppRunner.cpp:4686:22 #24 XREMain::XRE_main(int, char**, mozilla::BootstrapConfig const&) /src/toolkit/xre/nsAppRunner.cpp:4848:8 #25 XRE_main(int, char**, mozilla::BootstrapConfig const&) /src/toolkit/xre/nsAppRunner.cpp:4943:21 #26 do_main(int, char**, char**) /src/browser/app/nsBrowserApp.cpp:231:22 #27 main /src/browser/app/nsBrowserApp.cpp:304:16 #28 __libc_start_main /build/glibc-bfm8X4/glibc-2.23/csu/../csu/libc-start.c:291 #29 _start (firefox+0x41ebe4)

Goes back more than a year, which is as far back as mozregression can bisect debug builds.