Add-on Compatibility for Firefox 27

Firefox 27 will be released on February 4th. This release cycle is slightly longer due to the holidays. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 27 for Developers, so you should read that too.

General

• Do away with downloads-indicator. The downloads-button and downloads-indicator nodes were serving the same purpose, so the former was kept and the latter was removed. If you’re using downloads-indicator in your JS or CSS code, make sure to replace it with downloads-button.
• [OS.File] Inconsistent cross-platform behavior due to O_APPEND. If you’re using the OS.File library, opening files on non-Windows systems would have opened them with the append option on by default, while not so on Windows. This change makes all file open calls not append by default.
• Findbar for Stylish editor is broken. If your extension includes a view which uses a findbar, it may be broken on 27. The details about this change can be found on bug 939381.
• Remove -moz-rgba() and -moz-hsla(). The unprefixed CSS functions should be used instead.

XPCOM

• Stop exporting JS symbols in Firefox. JSAPI is no longer available to extensions, which should only really be a problem for very specific binary add-ons. There are better ways to run JS in your extension anyway.

New!

• Need a way to create invisible, permanent docshell. If you’re currently using the hidden DOM window or another hack to keep a hidden DOM structure, you might want to give this one a look. With createWindowlessBrowser, you can create a hidden content or chrome window.
• Add log4moz.js to toolkit as Log.jsm. log4moz is a very useful logging tool based on its popular Java counterpart, log4j. It has existed in various forms along the years, but now it is very easily accessible using Log.jsm.
• Expose DOM URL to js modules. You can now access the URL global constructor from a JSM.
• Command line option -jsconsole should open the Browser Console. Like it used to be possible with the old Error Console, now you can invoke the Browser Console from the command line.
• [OS.File] Add a function to recursively remove directories.
• Option to deobfuscate JavaScript in the debugger.

Please let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 27, I’d like to know.

The automatic compatibility validation and upgrade for add-ons on AMO will happen very soon, so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 26.