Firefox 4 - new features explained in detail

Back to the front of the pack: Ars reviews Firefox 4
Ars Technica reviews the major new features of Firefox 4.

The link above has some tips on adjusting things more to your liking. See the link below for more tips:
Lifehacker: How to fix annoyances with Firefox 4's new look

New Facebook Messages feature rolling out and causing confusion

Facebook is currently rolling out a new message feature that combines chat, messages, txt messages, and email. They are also offering a Facebook email address as part of all this.
I haven't got this feature yet, so I can't comment on it from personal experience.

Here are some links that may help:

Facebook blog: See the Messages That Matter
This is Facebook's explanation of how the new feature is supposed to work.

Facebook's help page about this topic

Both these above links from Facebook will point you toward the Tour. But it tells you practically nothing.

Reviews and news about the new feature:
Facebook's new messaging feature raises privacy questions

Facebook's new features, but borking up the site in the process

Enable HTTPS for Facebook

How to Enable and Set Facebook Secure HTTPS Login | Web Talk
This post (above) takes you through the steps to always log into Facebook with a more secure connection.
Basically, go to Accounts, account security, change, and check off the Browse Facebook on a secure connection (https) whenever possible checkbox.

Restore Default Enter Key Behaviour in Facebook Comments

Restore Default Enter Key Behavior In Facebook Comments | Better Facebook
Want to be able to use Enter instead of Shift+Enter to add a new line in your comment in Facebook. Currently, with the new behaviour in FB, Pressing Enter while typing a comment posts the comment.
The the add-ons available at this site (above), you can restore the Comment button and the normal behaviour of the Enter key.