In bug 1355569, we are looking to enable Screenshots during unit test runs. On try we're hitting this error: https://treeherder.mozilla.org/logviewer.html#?job_id=92425763&repo=try&lineNumber=3933 1INFO - TEST-UNEXPECTED-FAIL | browser/base/content/test/general/browser_tabopen_reflows.js | unexpected uninterruptible reflow '<stack>' - INFO - Stack trace: INFO - chrome://mochitests/content/browser/browser/base/content/test/general/browser_tabopen_reflows.js:reflow:136 INFO - chrome://browser/content/ext-utils.js:get width:528 INFO - resource://gre/modules/ExtensionTabs.jsm:convert:470 INFO - chrome://browser/content/ext-tabs.js:fireForTab:239 INFO - chrome://browser/content/ext-tabs.js:statusListener:283 INFO - resource://gre/modules/ExtensionTabs.jsm:onStateChange:1116 INFO - chrome://browser/content/tabbrowser.xml:callListeners:492 INFO - chrome://browser/content/tabbrowser.xml:_callProgressListeners:513 INFO - chrome://browser/content/tabbrowser.xml:_callProgressListeners:563 INFO - chrome://browser/content/tabbrowser.xml:onStateChange:757 INFO - chrome://browser/content/browser.js:_loadURIWithFlags:1011 INFO - chrome://browser/content/tabbrowser.xml:loadURIWithFlags:7833 INFO - chrome://browser/content/tabbrowser.xml:addTab:2365 INFO - chrome://browser/content/tabbrowser.xml:loadOneTab:1522 INFO - chrome://browser/content/utilityOverlay.js:openLinkIn:436 INFO - chrome://browser/content/utilityOverlay.js:openUILinkIn:194 INFO - chrome://browser/content/browser.js:BrowserOpenTab:2145 INFO - chrome://mochitests/content/browser/browser/base/content/test/general/browser_tabopen_reflows.js:null:105 INFO - Tester_execTest@chrome://mochikit/content/browser-test.js:752:9 INFO - Tester.prototype.nextTest</<@chrome://mochikit/content/browser-test.js:672:7 INFO - SimpleTest.waitForFocus/waitForFocusInner/focusedOrLoaded/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:791:59

STR: 1) Use latest mozilla-central. 2) In testing/profiles/prefs_general.js, apply the change: -user_pref("extensions.screenshots.system-disabled", true); +user_pref("extensions.screenshots.system-disabled", false); 3) Run the test ./mach test browser/base/content/test/general/browser_tabopen_reflows.js Results as per comment 0. Although we're picking this up due to enabling Screenshots, I suspect this could happen with other user-installed WebExtensions that do things with tabs.

This may have been fixed by bug 1358415. Can you confirm?

(In reply to Mike Conley (:mconley) from comment #2) > This may have been fixed by bug 1358415. Can you confirm? Thanks for the pointer. Running on try seems to confirm that this has gone away, so I'll count it as a dupe of that bug.