Mozilla has published a blog and sent out an e-mail notifying users of what seems to be a relatively minor security breach. User IDs and password hashes for users were available for public access briefly.  Users who have not been active before April 2009, however, had their password hashes stored in MD5 hashes which could be retrieved via password cracking.  This method of storing passwords has been retired by Mozilla which is why users who logged in after April 2009 are safe.

The problem would come in for those users who use the same password across multiple sites (particularly the same password to access the e-mail account they registered with).

As a quick tip, we all have dozens (at least) of "low-impact" sites we have passwords for: new sites, blogs, etc.  The impact of those accounts being compromised is trivial, at best.  However, if the same password is used (and that password is mapped to an e-mail address or username) it can be used to access other, more sensitive accounts.  You could have a different password for each site, which quickly becomes impractical.  Sites using centralized logins are few and far-between (say Open ID).  A solution I've tried to use is to have an insecure password but salt it with some designation for the site I'm accessing.  Say the insecure password is qwerty.  I can add two characters designating what I'm accessing for each site.  So qwertyFF (FF for Firefox) for addons.mozilla.org.  This allows for different passwords at each site, but in a way that is easy to remember multiple passwords.  Obviously, you won't want to user "qwerty" as the base for those passwords, but you get the idea.

Update: To clarify, when I say "insecure password" above, I mean for a low-impact site on no consequence, not an insecure password in the sense of a weak one.  True random passwords are better, but if we have 100 different logins, that's not practical for the 95 of those logins that simply don't matter.

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John Bambenek
bambenek at gmail /dot/ com