Firefox 47 will be released on June 7th. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 47 for Developers, so you should also give it a look.

General

• Remove FUEL. The FUEL library has been deprecated since Firefox 40.
• Remove the about:customizing preloading hack. The UI customization panel no longer opens using the about:customizing URL.
• Move gDevTools.jsm to a commonjs module. Instead of loading the module using Cu.import, you should now use
  require("devtools/client/framework/devtools-browser");. The module still works for backward compatibility, but it will be removed in the future.
• Don’t let web pages link to view-source: URLs.

Tabs

• TabOpen and TabClose events should provide more detail about tabs moved between windows.
• Remove tabs’ visibleLabel property and TabLabelModified event. This is a reversal from previous work on supporting a separate label for tabs.

XPCOM

• CookieManager should remove cookies only if they match the userContextId. This changes
  nsICookieManager.remove by adding a new required argument (originAttributes). Update: these changes may be temporarily reverted in bug 1259169, but you should still prepare for them.
• Various changes to nsIX509CertDB: bug 1064402, bug 1241646, bug 1241650. Many functions changed here, so I won’t list them.
• Remove uses of nsIEnumerator from PSM. This changes the functions listTokens, listModules, and listSlots, both of which now return nsISimpleEnumerator instead of nsIEnumerator.
• Remove uriIsPrefix option from nsINavHistoryQuery.
• Replace removeVisitsTimeframe with History.removeVisitsByFilter and deprecate it.

New

• Debugging auto-close XUL panels is painful. Now you can debug popup panels in add-ons.
• Support frames similar to mozbrowser on desktop Firefox. This enables a new iframe API that makes the content believe it’s being loaded in a top-level window.

Let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 47, I’d like to know.

The automatic compatibility validation and upgrade for add-ons on AMO will happen in a few weeks, so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 46.