Firefox 4 is coming together steadily with another beta build now available. Mozilla pushed out Firefox 4 Beta 3 earlier today, which the organization has deemed stable and cleared for standard use. We would mostly agree with that, having used the first and second beta versions extensively. Personally, I've only experienced a handful of bugs which seem to be Flash-related, and they're uncommon anyhow.
Previous versions of the Firefox 4 beta should automatically update to beta 3, but you download a standalone installer here. At least two more betas are planned for the greatly overhauled browser, with the final build scheduled for November. Be sure to check out our compendium of Firefox 4 beta tweaks, and don't hesitate to share your own.