GECKO(21899) | [Child 21902] WARNING: stylo: this @import rule was not constructed: file /Volumes/mozilladev/mozilla-central/layout/style/ServoCSSRuleList.cpp, line 153 GECKO(21899) | [Child 21902] WARNING: stylo: this @import rule was not constructed: file /Volumes/mozilladev/mozilla-central/layout/style/ServoCSSRuleList.cpp, line 153 GECKO(21899) | ************************* GECKO(21899) | A coding exception was thrown and uncaught in a Task. GECKO(21899) | Full message: TypeError: rule is null GECKO(21899) | Full stack: _getImported/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/server/actors/stylesheets.js:930:9 GECKO(21899) | _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:311:39 GECKO(21899) | process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:922:23 GECKO(21899) | walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:806:7 GECKO(21899) | Promise*scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:739:11 GECKO(21899) | schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:770:7 GECKO(21899) | Promise.prototype.then@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:455:5 GECKO(21899) | _handleResultValue@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:387:7 GECKO(21899) | _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:319:13 GECKO(21899) | TaskImpl@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:273:3 GECKO(21899) | asyncFunction@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:247:14 GECKO(21899) | spawn@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:161:12 GECKO(21899) | _getImported@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/server/actors/stylesheets.js:923:12 GECKO(21899) | _addStyleSheets/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/server/actors/stylesheets.js:905:29 GECKO(21899) | _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:311:39 GECKO(21899) | TaskImpl@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:273:3 GECKO(21899) | asyncFunction@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:247:14 GECKO(21899) | spawn@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:161:12 GECKO(21899) | _addStyleSheets@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/server/actors/stylesheets.js:878:12 GECKO(21899) | StyleSheetsActor<.getStyleSheets<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/server/actors/stylesheets.js:830:26 GECKO(21899) | _run@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:311:39 GECKO(21899) | TaskImpl@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:273:3 GECKO(21899) | asyncFunction@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/task.js:247:14 GECKO(21899) | handler@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/protocol.js:1082:19 GECKO(21899) | onPacket@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/server/main.js:1760:15 GECKO(21899) | receiveMessage@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/transport/transport.js:761:7 GECKO(21899) | *************************

I believe this one may be fixed once bug 1367213 is fixed.

I don't think bug 1368381 will be enough, we had the same error filed as bug 1357724 where :xidorn suspects it's because we don't have all rule types implemented yet. I'll dupe this over there and copy the dependency.