Important note If you are a end-user, you are probably not affected. This is a call to add-on developers.

Developers of the following add-ons will need to update said add-ons to make them compatible with Firefox 25(update: we’re giving you some more time to fix stuff, so Firefox 27). Otherwise, these add-ons will most likely break:

MSN For Firefox

Bing For Firefox

Twitter

Tab Mix Plus

IE Tab

Undo Closed Tabs Button

SessionPage

Tab Scope

Taboo

Tree Style Tab

New Tab JumpStart

TabGroups Manager

Browse Periodically

Tab Utilities

Tile Tabs

IE Tab 2

Vertical Tabs

Master Password+

Home Dash

Extension Test

Progress Bar on Tab

Fox Splitter

Dormancy

Tabkit 2nd Edition

UnloadTab

Tabby2

Tab Restore

Side Tabs

Home Dash Lite-Dial

Fire IE

Tab Utilities Lite CustomEdition

Tabulous

Bar Tab Lite X

PageExpand

IE Tab 2 (SeaMonkey)

All Tabs Helper

multiplaceHolder

Suspend Tabs

All of these add-ons tap directly into undocumented, internal data structures that will disappear in the near future (expected: Firefox 27). If you are the author or maintainer of one of these add-ons, you should monitor carefully bug 874381 and its blockers for all technical details.

If you need technical help or if you need us to provide alternative public APIs, please get in touch as soon as possible.

Edit Added Suspend Tabs.

Edit Postponed to Firefox 27.

Edit I should have given more details about what exactly will break. We are progressively getting rid of all fields whose name starts with __SS. These add-ons are the add-ons that depend on such fields.

Edit Added a clarification about the audience of this blog post.