A tipster just e-mailed me news of another Firefox add-in. Ho-hum. What does that make - 2 billion?
Oh. Wait. This one's different:
Blog This for Firefox adds a button to Firefox which starts a new Windows Live Writer blog post prepopulated with content and title from the current web page.
The real shock is that this add-in was written by Microsoft employees and posted on Microsoft servers, at the Windows Live Gallery. It works, too. (I'm composing this post in Windows Live Writer after clicking the Blog This button from Firefox 18.104.22.168.)
Firefox purists will complain that it was written as a Windows Installer package rather than being distributed as a Firefox extension. But that's not such a big deal. Windows Live Writer runs only on Windows, after all, so anyone capable of using this extension is perfectly capable of running the executable.
Let's see: Microsoft adopts the Firefox RSS icon for IE7. Mozilla hires the ex-Microsoft employee who shipped Windows XP Service Pack 2 as security head for Firefox. Microsoft invites Firefox team to Redmond for Vista hands-on help, and they accept.
They're just not doing browser wars like they used to.
Update 29-Sep: Microsoft also released a new (beta) version of Windows Live Writer this week.