“The vulnerability is caused due to an error in the handling of an URL that contains the 0xAD character in its domain name. This can be exploited to cause a heap-based buffer overflow.
Successful exploitation crashes Firefox [and these other browsers] and may potentially allow code execution but requires that the user is tricked into visiting a malicious web site or open a specially crafted HTML file.”
So don't browse untrusted websites until they release a fix.
Check these URLs f u think you are affected:-