Take a look here, the firefox tag page:
As far as I know this is Firefox official logo: (original)
I'm pretty sure it used to be that official logo until recently but now it's suddenly changed to blue and toothless theme of Mozilla foundation. (This appears to be the original)
I wouldn't really mind unless discovering another oddity: that new logo is hosted on imgur, while all other sponsored tag icons I encountered are hosted on http://cdn.sstatic.net e.g. android logo url is http://cdn.sstatic.net/stackoverflow/img/tag-logo-android.png and facebook logo url is http://sstatic.net/stackoverflow/img/tag-logo-facebook.png
So who is responsible for those icons? Has Mozilla foundation itself decided to change the logo?