Add-on Compatibility for Firefox 35

Firefox 35 will be released on January 13th. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 35 for Developers, so you should also give it a look.

General

• Implement ES6 “temporal dead zone” for let. If your add-on is affected by this, you were likely contacted by us before about this, since it affected many add-ons and caused their scripts not to work at all. This is due to certain types of redeclaration using let that weren’t detected before. There’s an extended discussion about how this in the newsgroups.
• Truncate tag to a maximum length. Tags in bookmarks used to have no length restrictions, causing performance problems if they were too long. They are now restricted to to 100 characters.
• Remove DOS encodings that aren’t Web-exposed. A number of old encodings that weren’t exposed to content have been removed.
• Replace jschar typedef with char16_t.
• Remove Navigator::MozisLocallyAvailable API.

New!

• tabbrowser’s _getTabForBrowser is very slow with lots of tabs. The new bit here is that now there’s a public getTabForBrowser function in gBrowser, which is also more efficient when there are lots of tabs open. The private form of this function (_getTabForBrowser, with an underscore) is deprecated.

Please let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 35, I’d like to know.

The automatic compatibility validation and upgrade for add-ons on AMO will happen soon, so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 34.