This is causing two test failures in devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js 55 INFO TEST-UNEXPECTED-FAIL | devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js | .boxmodel-margin.boxmodel-left > span has the right value. - Got auto, expected 0 Stack trace: chrome://mochikit/content/browser-test.js:test_is:967 chrome://mochitests/content/browser/devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js:testInitialValues:117 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 @chrome://mochitests/content/browser/devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js:104:24 TaskImpl_run@resource://gre/modules/Task.jsm:331:42 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 WalkerFront<.querySelector<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/fronts/inspector.js:621:12 getNodeFront@chrome://mochitests/content/browser/devtools/client/inspector/test/shared-head.js:179:10 @chrome://mochitests/content/browser/devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js:103:20 TaskImpl_run@resource://gre/modules/Task.jsm:331:42 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 updateBoxModel/lastRequest<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/inspector/boxmodel/box-model.js:162:34 _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:311:39 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 updateBoxModel/lastRequest<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/inspector/boxmodel/box-model.js:151:38 _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:311:39 56 INFO TEST-UNEXPECTED-FAIL | devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js | .boxmodel-margin.boxmodel-right > span has the right value. - Got auto, expected 0 Stack trace: chrome://mochikit/content/browser-test.js:test_is:967 chrome://mochitests/content/browser/devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js:testInitialValues:117 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 @chrome://mochitests/content/browser/devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js:104:24 TaskImpl_run@resource://gre/modules/Task.jsm:331:42 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 WalkerFront<.querySelector<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/fronts/inspector.js:621:12 getNodeFront@chrome://mochitests/content/browser/devtools/client/inspector/test/shared-head.js:179:10 @chrome://mochitests/content/browser/devtools/client/inspector/boxmodel/test/browser_boxmodel_pseudo-element.js:103:20 TaskImpl_run@resource://gre/modules/Task.jsm:331:42 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 updateBoxModel/lastRequest<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/inspector/boxmodel/box-model.js:162:34 _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:311:39 process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:707:7 onPacket/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1329:9 DevTools RDP*request@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1269:14 generateRequestMethods/</frontProto[name]@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1426:14 updateBoxModel/lastRequest<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/inspector/boxmodel/box-model.js:151:38 _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:311:39

I have a feeling that this has to do with the following line: http://searchfox.org/mozilla-central/rev/8a61c71153a79cda2e1ae7d477564347c607cc5f/layout/style/nsComputedDOMStyle.cpp#565

Seems like the same issue also affects: * devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js

Assigning for now, on the assumption that bug 1381083 also fixes this.

These tests appear fixed, yay! :D