Mozilla , one day after , because of a vulnerability that potentially allowed malicious Web pages to read the URLs of other websites accessed by visiting users. Such behavior should normally be prohibited by the browser's security mechanisms.

The issue by security researcher Gareth Heyes on Wednesday. Heyes published proof-of-concept code that, when loaded from an arbitrary Web page, could determine the user name of a user logged into Twitter.

Mozilla determined that the issue found by Heyes only affects Firefox 16.0 and addressed it in Firefox 16.0.1.

However, the new version of Firefox also fixes a separate vulnerability discovered by a Mozilla security researcher that can result in a similar behavior. In Firefox 15 and earlier versions this second security issue can also potentially lead to arbitrary code execution.

In addition, Firefox 16.0.1 fixes two memory corruption bugs in the browser engine that can result in crashes and can potentially be exploited to execute arbitrary code. One of these bugs only affects the Android version of Firefox when running inside custom Android firmware like CyanogenMod.