Two vulnerabilities have been discovered in Firefox, which can be exploited by malicious people to conduct cross-site scripting attacks and compromise a user's system.
Successful exploitation requires that the site is allowed to install software (default sites are "update.mozilla.org" and "addons.mozilla.org").
A combination of vulnerability 1 and 2 can be exploited to execute arbitrary code.
NOTE: Exploit code is publicly available.
The vulnerabilities have been confirmed in version 1.0.3. Other versions may also be affected.
2) Disable software installation: Options --> Web Features --> "Allow web sites to install software"
NOTE: A temporary solution has been added to the sites "update.mozilla.org" and "addons.mozilla.org" where requests are redirected to "do-not-add.mozilla.org". This will stop the publicly available exploit code using a combination of vulnerability 1 and 2 to execute arbitrary code in the default settings of Firefox.