I wrote an extension with a very simple XUL overlay which is causing fatal (JS) asserts in debug builds: stack: #2 0x00007ffff68c10f7 in js::CompartmentChecker::fail (c1=0x7fffe81b5000, c2= 0x7fffe2850800) at ../../../src/js/src/jscntxtinlines.h:541 #3 0x00007ffff68c1165 in js::CompartmentChecker::check (this=0x7fffffffc9d0, c=0x7fffe2850800) at ../../../src/js/src/jscntxtinlines.h:549 #4 0x00007ffff68c1377 in js::CompartmentChecker::check (this=0x7fffffffc9d0, script=0x7fffe5c15980) at ../../../src/js/src/jscntxtinlines.h:595 #5 0x00007ffff68c5847 in js::assertSameCompartment<JSObject*, JSScript*> (cx= 0x7fffe488f400, t1=0x7fffe5d37d80, t2=0x7fffe5c15980) at ../../../src/js/src/jscntxtinlines.h:634 #6 0x00007ffff68b8524 in JS_ExecuteScript (cx=0x7fffe488f400, obj= 0x7fffe5d37d80, script=0x7fffe5c15980, rval=0x7fffffffcab0) at ../../../src/js/src/jsapi.cpp:4834 #7 0x00007ffff591aab7 in nsJSContext::ExecuteScript (this=0x7fffe486bbe0, aScriptObject=0x7fffe2634120, aScopeObject=0x7fffe5d37d80, aRetValue=0x0, aIsUndefined=0x0) at ../../../src/dom/base/nsJSEnvironment.cpp:1899 #8 0x00007ffff58ee537 in nsXULDocument::ExecuteScript (this=0x7fffe47b8800, aContext=0x7fffe486bbe0, aScriptObject=0x7fffe2634120) at ../../../../../src/content/xul/document/src/nsXULDocument.cpp:3622 #9 0x00007ffff58ee773 in nsXULDocument::ExecuteScript (this=0x7fffe47b8800, aScript=0x7fffe472ac80) at ../../../../../src/content/xul/document/src/nsXULDocument.cpp:3645 #10 0x00007ffff58ec183 in nsXULDocument::ResumeWalk (this=0x7fffe47b8800) at ../../../../../src/content/xul/document/src/nsXULDocument.cpp:2995 #11 0x00007ffff58e4403 in nsXULDocument::OnPrototypeLoadDone (this= 0x7fffe47b8800, aResumeWalk=1) at ../../../../../src/content/xul/document/src/nsXULDocument.cpp:647 #12 0x00007ffff58e4342 in nsXULDocument::EndLoad (this=0x7fffe47b8800) at ../../../../../src/content/xul/document/src/nsXULDocument.cpp:630 #13 0x00007ffff58dd8dc in XULContentSinkImpl::DidBuildModel (this= 0x7fffe2bf2c80, aTerminated=0) at ../../../../../src/content/xul/document/src/nsXULContentSink.cpp:277 #14 0x00007ffff51cb63c in nsParser::DidBuildModel (this=0x7fffe29de380, anErrorCode=0) at ../../../../src/parser/htmlparser/src/nsParser.cpp:1588 #15 0x00007ffff51cd518 in nsParser::ResumeParse (this=0x7fffe29de380, allowIteration=1, aIsFinalChunk=1, aCanInterrupt=1) at ../../../../src/parser/htmlparser/src/nsParser.cpp:2367 #16 0x00007ffff51cf42c in nsParser::OnStopRequest (this=0x7fffe29de380, ---Type <return> to continue, or q <return> to quit--- request=0x7fffe39ded60, aContext=0x0, status=0) at ../../../../src/parser/htmlparser/src/nsParser.cpp:3000 #17 0x00007ffff518eb0a in nsJARChannel::OnStopRequest (this=0x7fffe39ded60, req=0x7fffe2bf2d00, ctx=0x0, status=0) at ../../../src/modules/libjar/nsJARChannel.cpp:906 #18 0x00007ffff500d4a0 in nsInputStreamPump::OnStateStop (this=0x7fffe2bf2d00) at ../../../../src/netwerk/base/src/nsInputStreamPump.cpp:578 #19 0x00007ffff500cd3a in nsInputStreamPump::OnInputStreamReady (this= 0x7fffe2bf2d00, stream=0x7fffe2842588) at ../../../../src/netwerk/base/src/nsInputStreamPump.cpp:403 #20 0x00007ffff66cce09 in nsInputStreamReadyEvent::Run (this=0x7fffe4860040) at ../../../src/xpcom/io/nsStreamUtils.cpp:112 #21 0x00007ffff66f8158 in nsThread::ProcessNextEvent (this=0x7fffec103cc0, mayWait=0, result=0x7fffffffd19c) at ../../../src/xpcom/threads/nsThread.cpp:626 #22 0x00007ffff66820b0 in NS_ProcessNextEvent_P (thread=0x7fffec103cc0, mayWait=0) at nsThreadUtils.cpp:250 #23 0x00007ffff64c8236 in mozilla::ipc::MessagePump::Run (this=0x7fffec10f4c0, aDelegate=0x7fffec1261c0) at ../../../src/ipc/glue/MessagePump.cpp:110 #24 0x00007ffff6761ebb in MessageLoop::RunInternal (this=0x7fffec1261c0) at ../../../src/ipc/chromium/src/base/message_loop.cc:219 #25 0x00007ffff6761e40 in MessageLoop::RunHandler (this=0x7fffec1261c0) at ../../../src/ipc/chromium/src/base/message_loop.cc:202 #26 0x00007ffff6761dd1 in MessageLoop::Run (this=0x7fffec1261c0) at ../../../src/ipc/chromium/src/base/message_loop.cc:176 #27 0x00007ffff63625ef in nsBaseAppShell::Run (this=0x7fffe8195400) at ../../../../src/widget/src/xpwidgets/nsBaseAppShell.cpp:181 #28 0x00007ffff60a8ab9 in nsAppStartup::Run (this=0x7fffe81a9ce0) at ../../../../../src/toolkit/components/startup/src/nsAppStartup.cpp:191 #29 0x00007ffff4fb89ba in XRE_main (argc=5, argv=0x7fffffffddf8, aAppData= 0x7ffff2e27080) at ../../../src/toolkit/xre/nsAppRunner.cpp:3691 #30 0x0000000000401cff in main (argc=5, argv=0x7fffffffddf8) at ../../../src/browser/app/nsBrowserApp.cpp:158 I'll attach the extension XPI, I'm using in a sec, but I suspect that the problem may be caused because I'm loading the overlay from a file: URI instead of a chrome: URI, and it has a <script>.

The purpose of this extension is to crash a jetpack process to collect a crash report, but that's unimportant to the issue here.

Reproduced. Awesome test case bsmedberg. Sorry for not following up on this sooner.