Current Nightly, which on version 45 has caused some add-ons to stop functioning. Some of the affected add-ons were: AdBlockPlus, Classic Toolbar Buttons, OmniSidebar, FindBar Tweak.

If you’re using Firefox Nightly, you can make those add-ons work again by adding contentaccessible=yes parameter to the each affected add-on’s Chrome.mainfest file.or wait for Mozilla to fix this bug or developers to release an update for their not-working add-ons to address the issue.

AdblockPlus doesn't work in Firefox 45 and shows the error