The flaw means that vulnerable versions of the browsers will crash when visiting maliciously constructed web sites containing overly long (more than 256 bytes) URLs. Successful exploitation of this heap-based buffer overflow flaw creates a means for hackers to load malware onto the machines of visiting surfers.
It's being listed as “moderate”, and does not affect the newest version nor versions 8 and prior. If you are using 9.0 or 9.01, it's a good idea to upgrade. Whether you are using the Windows or Linux build, you are vulnerable.