An upgrade of the Firefox open-source browser has been pulled after 24 hours due to a critical security bug.
Version 16 of the browser was released on Tuesday, but after a vulnerability was discovered the software was yanked offline.
In a blog post, the non-profit foundation which operates Firefox, Mozilla, said:
"The vulnerability could allow a malicious site to potentially determine which websites users have visited and have access to the URL or URL parameters. At this time we have no indication that this vulnerability is currently being exploited in the wild."
Michael Coates, director of security at Mozilla, added that users could downgrade on their website until the issue was fixed.
No users were upgraded automatically to the new version, Mozilla said.
Recently Firefox has fallen to third place in the so-called 'browser wars' behind Google Chrome and Microsoft's resilient - in market share terms - Internet Explorer in first.
Firefox had a 20% share of desktop browsers in September, according to Net Applications. Internet Explorer had around 54% and Chrome just under 19%.