Mozilla has released fixes for five security holes in older versions of Firefox, while a security company has warned of a zero-day flaw in the latest version of the popular browser.

The five flaws addressed by Mozilla included three the company rated 'critical'. These three flaws involve an error in handling out-of-memory conditions; stability errors in the Gecko rendering engine; and a bug in the way Mozilla's implementation of web workers handles posted messages, Mozilla said. Web workers are used to carry out scripting tasks in a way that reduces the processing load on the user interface.

All three of these bugs can potentially be used to execute malicious code and take over a user's system, Mozilla said.

The two remaining flaws are less serious, potentially allowing an attacker to execute malicious JavaScript code.