Following reports earlier this week regarding a newly discovered flaw in Firefox, the Mozilla team today confirmed the bug. The flaw revolves around the way certain types of add-ons are installed, in particular add-ons that store information inside Javascript files. Ultimately, the flaw could lead to information being compromised, or, more rarely, the system.
Mozilla has classified the threat as "low risk", so they are probably not working on an emergency fix. It is likely we'll see it fixed with the next release of Firefox. At least we hope. You can read more about the bug on Bugzilla.