This started when bug 688981 landed on mozilla-central and inbound. https://tbpl.mozilla.org/php/getParsedLog.php?id=13952435&tree=Mozilla-Inbound Rev4 MacOSX Lion 10.7 mozilla-inbound opt test mochitest-other on 2012-07-29 16:03:28 PDT for push 36c30260e7fa slave: talos-r4-lion-014 TEST-START | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | positionConsole() is available TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | menuitem for above positioning calls positionConsole() correctly TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | menuitem for below positioning calls positionConsole() correctly TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | menuitem for window positioning calls positionConsole() correctly TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | initial console position is correct TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | position menu checkbox is below TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | pref is below TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | web console position changed to 'above' TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | above position is correct TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | position menu checkbox is above TEST-PASS | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | pref is above TEST-UNEXPECTED-FAIL | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | Timed out while waiting for: web console position changed to 'window' Stack trace: JS frame :: chrome://mochitests/content/browser/browser/devtools/webconsole/test/head.js :: wait :: line 241 JS frame :: chrome://mochitests/content/browser/browser/devtools/webconsole/test/head.js :: <TOP_LEVEL> :: line 251 native frame :: <unknown filename> :: <TOP_LEVEL> :: line 0 INFO TEST-END | chrome://mochitests/content/browser/browser/devtools/webconsole/test/browser_webconsole_position_ui.js | finished in 5449ms

Green try runs: https://tbpl.mozilla.org/?tree=Try&rev=21fb97db3316 Explanation: 1. I made changes so I was able to repro the failure on my system. 2. Found that the iframe onload event fires before popupshown (window positioning), so some code never executed - the test waited 5 seconds for specific changes in the HUD object, then timed out. The _afterPositionConsole() method added the load event listener in the popupshown event handler. 3. Solution: add the onload event listener before we move the iframe element in the DOM, not after. Results are green after 50+ repeated runs on my system. Also green on try servers.

Comment on attachment 648361 [details] [diff] [review] proposed fix R+++++++!!!

<3 Thank you!