Firefox 11 was pushed to the Aurora channel weeks ago, and Firefox 12 will follow suit very soon. So, it’s time for the long overdue overview of bugs that can affect add-on compatibility in Firefox 11. I’m sorry this update is being posted so late, but things have been pretty crazy lately. More on that in the Firefox 10 section.

A few notes regarding Firefox 10

If everything goes according to plan, Firefox 10 will be pushed to the public in less than a week. There are a couple of points that are worth mentioning:

• Starting with Firefox 10, add-ons will default to compatible. All add-on versions that have compatibility up to Firefox 4 or higher will automatically work in Firefox 10 and all future releases. This excludes add-ons that are not extensions (themes, dictionaries, language packs) and add-ons with binary components. We will also keep an override list that we will fill with all add-on versions that are known to break due to compatibility problems. This is what has kept me busy for the past weeks. We need your help to keep the override list up to date.
  
• Rename omni.jar to omni.ja. If your add-on references omni.jar directly, it will break now that it has been renamed. We recommend that you find more flexible ways to reference these files, since most should be accessible through chrome URLs.

For more information about Firefox 10 compatibility, please read the full compatibility update.

Firefox 11

• Remove the no-argument form of requestAnimationFrame. This function now takes one mandatory argument.
• Remove nsIDOMNSElement. This affects many SDK-based (Jetpack) add-ons using old versions of the SDK. We encourage you to update to the latest stable version as soon as possible.
• Remove the crazy navigator preservation behavior. If your add-on sets expando properties to the navigator object in web pages and relies on them keeping their state while navigating within the same domain, this concerns you.
• Remove ‘countryCode’ from nsIDOMGeoPositionAddress.idl. The non-standard countryCode property was removed.
• Kill dynamic containers. This is an obscure feature that was added to the bookmarks code but it was rarely used.
• Remove nsICharsetResolver.

Other important changes are noted in Firefox 11 for developers.

New stuff in 11!

• Support HTML parsing in XMLHttpRequest. The documentation page for this feature is being written at the moment, but it already has useful info.
• Sync add-ons. It seems Firefox Sync will be able to sync installed add-ons across devices. I doubt it will be able to sync all of your add-on configuration if your add-on writes custom files in the profile or elsewhere, though.
• Add a scriptable way to set a dock badge text. For Mac OS add-ons that want to write to the dock icon.

Please let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 10 or 11, I’d like to know.

Because of the Default to Compatible feature, we are no longer doing compatibility bumps like we did before. We will still run the validation but only send you a message if your add-on is identified as incompatible. There will be no more automatic version upgrades, given that there’s no point anymore.