Anecdotally, I have an oddly large population of vistors to my site with Firefox 9. I don't know what changes were made to how Firefox updates around that time. But it seems like the update train has unwittingly left few users behind.
As a reference, Firefox 9 is the version in the packages repo for FreeBSD 9.0-STABLE and it's probably the same for a fair number of other oses that peg versions on release.
