Mozilla has released beta 6 of Firefox 4. This update is a stability release containing several bug fixes, including one that resulted in crashes for Windows users.
Given that this release comes just a week after beta 5, I think that we are now getting close to a release candidate. Although not just yet - it seems that there's at least one more beta in the pipeline.
If running betas is your thing, I suggest upgrading to this latest release.
Release notes and download here.