The Firefox team is playing it safe.
There will be at least two more beta releases before a Firefox 4 release candidate is distributed, says one Firefox developer.
"We will release beta 10 as soon as possible during the week of the 24th ... we will release beta 11 as soon as possible during the week of the 31st, "says Christian Legnitto, in a message posted to the MozillaWiki. "To control risk for the RC the plan is to do two betas (10 and 11) rather than hold beta 10 for all betaN hardblockers."
There are more than 55 blockers that still need fixing and more than 318 bug fixes which need to be tested before the finished code is released.
Firefox 4 beta 9 was released on January 14. The first beta debuted on July 6.
Better safe than sorry.