Mozilla released the latest version of Firefox, version 126.96.36.199, this week, saying the update addresses a number of security and stability issues.
Mozilla notified users of 19 flaws in Firefox this week, 11 of which were called critical by the company.
The flaws allowed possible security bypasses, cross-site scripting, address spoofing, exposure of sensitive information, denial of service (DoS) attacks and system access, according to vulnerability monitoring firm Secunia.
Mozilla, in a statement posted Thursday on its website, urged users to upgrade for security reasons.
"Mozilla Corporation is also strongly recommending that Firefox 1.0 users upgrade to this latest release of Firefox 1.5 in order to take advantage of significant security and stability improvements," the company said. "Firefox 1.5 includes an automated update mechanism that ensures users are always up to date with the very latest updates."
Mozilla last issued vulnerability alerts in February over multiple highly critical flaws.
Meanwhile, Opera also released version 8.54 of its web browser this week. The open-source software was updated to address a buffer-overflow issue in handling cascading style sheets, according to the SANS Institute's Internet Storm Center website.