Firefox 155 release notes for enterprise admins

Firefox 155 Latest

Released 1 September 2026.

These changes apply to Firefox 155 and Firefox ESR 153.2.0 unless explicitly stated. Firefox ESR 153 is the current ESR.

DisableLaunchOnLogin: This policy prevents Firefox from launching automatically when the user logs in (Windows only in 155). Does not apply to the ESR. (bug 2001734)

SitePolicies: Added an HttpsOnly option to prevent specific sites from being loaded over HTTP. Firefox 155 only. (bug 2045980)
Captive portal and network connectivity checks now use firefox-portal-detection.com instead of detectportal.firefox.com. Network allowlists and proxy rules naming the old domain need updating. Firefox 155 only. (bug 2049252, bug 1898891)

ExtensionSettings: In Firefox 154 and Firefox ESR 153.1.0, configurations that quoted booleans ("true") would break and an invalid entry discarded the whole policy. The validator is relaxed to accept quoted booleans again, and invalid entries are now individually skipped. (bug 2065965)
SearchEngines: Contextual search prompted users to install a search engine when PreventInstalls was true. Firefox 155 only. (bug 2055614)
Locking legacy preferences such as pref.general.disable_button.default_browser didn't disable the corresponding controls in Firefox Settings, following the Settings rewrite. (bug 2056928, bug 2055887)
Firefox reported that it could pin itself to the taskbar when Windows Group Policy blocked pinning. Firefox 155 only. (bug 2059920)