This regression happened some time in the past week. It is the #3 most verbose warning during testing. It occurs most often in the |reftest/tests/layout/| tests. > 2202 [NNNNN] WARNING: Unexpected, plugin id not found!: file gfx/layers/ipc/CompositorChild.cpp, line 270 This warning [1], introduced in bug 1095754, shows up in the following test suites: > mozilla-central_ubuntu64_vm-debug_test-crashtest-e10s-bm122-tests1-linux64-build2.txt:2202 It shows up in 966 tests. A few of the most prevalent: > 42 - file:///builds/slave/test/build/tests/reftest/tests/layout/xul/tree/crashtests/585815.html > 37 - file:///builds/slave/test/build/tests/reftest/tests/layout/generic/crashtests/947158.html > 32 - file:///builds/slave/test/build/tests/reftest/tests/layout/style/crashtests/1164813-1.html > 19 - file:///builds/slave/test/build/tests/reftest/tests/layout/svg/crashtests/458453.html > 10 - file:///builds/slave/test/build/tests/reftest/tests/layout/mathml/crashtests/400157.xhtml > 8 - file:///builds/slave/test/build/tests/reftest/tests/layout/generic/crashtests/1134667.html > 7 - file:///builds/slave/test/build/tests/reftest/tests/widget/cocoa/crashtests/373122-1.html > 7 - file:///builds/slave/test/build/tests/reftest/tests/layout/generic/crashtests/786740-1.html > 6 - file:///builds/slave/test/build/tests/reftest/tests/layout/generic/crashtests/750066.html > 5 - file:///builds/slave/test/build/tests/reftest/tests/layout/xul/crashtests/344228-1.xul [1] https://hg.mozilla.org/mozilla-central/annotate/29b2df16e961/gfx/layers/ipc/CompositorChild.cpp#l270

I guess I should take this, pretty sure it's something I did.

This is now the #2 most verbose warning during testing.