Firefox 9 for Ubuntu 11.10 Oneiric
Until today Ubuntu 11.10 Oneiric is still on Firefox 8 and Thunderbird 8. And since WordPress is complaining about my Firefox version, I decided to upgrade to the Firefox 9.
Searching the web I came across this link, which unfortunately does not install Firefox 9, but the next version Firefox 10 b1 (which is logical since Firefox 9 is the current version, so the next version is Firefox 10).
The following link solves this problem by using the latest security release:
By the way, it is a pity that the firefox-stable release channel does not contain Oneiric Ocelot support and therefore breaks.
Update: this is described in this link: http://blog.dcxn.com/2011/06/28/quick-tip-keep-up-to-date-on-firefox-in-ubuntu/