Ignore removed listeners during dispatch.
Add `off` method to event/target for compatibility with devtools.
Foundation for browser & tab event handling.
Revert "Merge pull request #907 from jsantell/tabs-onready-for-non-html-671305"

This reverts commit 75f92ec7940f4012abd5d33c727b56cebe9ecf9e, reversing
changes made to bb071f7ac300d9a3d8227148153c892efc94f0b7.
Merge pull request #903 from Gozala/bug/tab-detraitifaction@854980

Bug 854980 - Implementing simple utils for observing window / tab events r=@Mossop
Fix bug 856403 - Upstream the indexed-db changes from 854323 to the SDK repository
Merge pull request #912 from KWierso/fixindexeddb

Fix bug 856403 - Upstream the indexed-db changes from 854323 to the SDK repo vidyo-r=mossop
Added pageshow and load events to tabs for bfcache/non-DOM content
Merge pull request #913 from jsantell/tabs-onready-for-non-html-671305

Fix bug 671305, Added pageshow and load events to tabs for bfcache/non-DOM content (resubmitting with non-timer dependent tests)
Revert "Merge pull request #913 from jsantell/tabs-onready-for-non-html-671305"

This reverts commit d5bc78c7aac210af764a08451e33215b11559c3e, reversing
changes made to ede336ee55ff8597d22e0ab101653fdb133ffc0a.
firefox-22 is now riding the trains, master is now destined to become firefox-23
 Added pageshow and load events to tabs for bfcache/non-DOM content, delay tests to work on all CI platforms
Bug 857598: Ensure waiting for session restore event before running the addon.
Remove unnecessary self from page-mod example
Update credits.md
Merge pull request #918 from jryans/master

Remove unnecessary self from page-mod example
Merge pull request #916 from ochameau/bug857598

Bug 857598: Ensure waiting for session restore event before running the addon. r=@mossop
Bug 857750 - TEST-UNEXPECTED-FAIL | tests/test-self.testSelf | self.loadReason is always `startup` on test runs ("install" != "startup")
Merge pull request #919 from ochameau/bug857750

Bug 857750 - TEST-UNEXPECTED-FAIL | tests/test-self.testSelf | self.loadReason is always `startup` on test runs ("install" != "startup") r=mossop
Bug 857750 followup - Change the versionInRange() check to account for the central->aurora merge earlier this week