Question 1

What is the EOL Risk Score for Firefox 155?

Accepted Answer

Firefox 155 has an EOL Risk Score™ of 65 out of 100, placing it in the High risk band. The score is calculated from four factors: EOL Recency (25/40), Attack Surface (10/30), CISA KEV Exposure (20/20), and Extended Support Availability (10/10).

Question 2

Is Firefox 155 still supported?

Accepted Answer

Firefox 155 is no longer supported — it has passed its end of life date (September 15, 2026). No further security patches will be issued. Upgrade to a supported version or obtain extended lifecycle support.

Question 3

When does Firefox 155 reach end of life?

Accepted Answer

Firefox 155 reached (or will reach) end of life on September 15, 2026. After this date, no security patches or bug fixes are issued by the vendor.

Question 4

What are the security risks of running Firefox 155 after end of life?

Accepted Answer

After end of life, the vendor's standard support for Firefox 155 ends, so newly discovered vulnerabilities may never be fixed unless a paid extended support option covers that version. Auditors ask about it too: PCI DSS requirement 12.3.4, for example, calls for a yearly review of vendor end-of-life announcements with a remediation plan approved by senior management.