browser/base/content/test/browser_pluginnotification.js and toolkit/mozapps/extensions/test/browser/browser_manualupdates.js fail on Windows 7 with 130078. Both tests use EventUtils.synthesizeMouse(element, 0, 0, ...) to send a click to element. I've had this fail before for me when writing a test (without 130078), so I think it is an existing problem, not something new with 130078. synthesizeMouse just gets the bounding client rect of the element, and then adds the passed in coords to the top left of it. If the element doesn't completely fill its bounding client rect the sent click could easily miss.