Firefox Extended Support Release (ESR) is a version of Firefox designed for organizations and environments where stability is more important than access to the latest features. If you're an IT administrator, developer targeting enterprise users, or someone who values absolute stability, ESR deserves attention.

What Firefox ESR Is

Mozilla maintains two release tracks simultaneously:

  • Firefox Rapid Release: new major version every 4 weeks (Firefox 130, 131, 132...)
  • Firefox ESR: major version updated roughly every 52 weeks, with minor updates (security patches, critical bug fixes) between

Current ESR cycle: Firefox ESR 128 (released June 2024, supported through approximately June 2025), with ESR 115 in its final months of overlap support.

Why ESR Exists

Enterprise environments can't easily update browsers every 4 weeks because:

  • Compatibility testing with internal web apps takes time
  • Group Policy/MDM rollout has its own scheduling
  • Some regulated industries require certification for software versions
  • Large-scale deployments need predictability

ESR gives IT teams a stable base to test against, with security updates but no behavioral changes within the ESR cycle.

Differences Between ESR and Rapid Release

Within an ESR cycle, the version:

  • Receives: security patches, critical bug fixes
  • Does not receive: new features, non-critical UI changes, new Web API implementations
  • Version numbering: ESR 128.4.0 means ESR based on Firefox 128, 4th minor update

When the ESR cycle ends and the next ESR begins (e.g., ESR 128 → ESR 136), organizations have an overlap period to migrate. Mozilla supports two ESR versions simultaneously during this transition.

Downloading Firefox ESR

Available from Mozilla's official download page. The ESR download is separate from the standard Firefox installer. Installs to a separate directory from rapid release Firefox so both can coexist.

On Linux:

# Debian/Ubuntu sudo apt install firefox-esr # Fedora/RHEL sudo dnf install firefox # Standard Fedora repo ships ESR in some configs

When to Use Firefox ESR

Good use cases:

  • Corporate environments with strict change control
  • Kiosk/digital signage deployments
  • Educational institutions (IT can't update daily)
  • Embedded browser use cases
  • Users who had something break with a rapid release update and need a stable base
  • Developers targeting enterprise users who will be on ESR

Not recommended for:

  • Developers who need the latest Web API implementations
  • Security-focused users who want the newest security research (rapid release gets security updates faster than ESR in some edge cases)
  • Personal use where you want new features

Deploying Firefox ESR in Enterprise

Windows Group Policy: Firefox (ESR specifically) supports full Group Policy via ADMX templates available from Mozilla. Set homepage, disable about:config, restrict extension installs, configure proxy settings — all via GPO.

Download the ADMX template from Mozilla's enterprise resources.

policies.json: a cross-platform alternative to GPO. Create distribution/policies.json in the Firefox installation directory:

{ "policies": { "DisableAppUpdate": true, "ExtensionSettings": { "*": { "blocked_install_message": "Contact IT for extension approval", "install_sources": ["https://addons.mozilla.org/"], "installation_mode": "blocked" }, "uBlock0@raymondhill.net": { "installation_mode": "force_installed", "install_url": "https://addons.mozilla.org/firefox/downloads/latest/ublock-origin/addon-latest.xpi" } }, "Proxy": { "Mode": "autoDetect" }, "OverrideFirstRunPage": "", "DisableTelemetry": true, "DisableFirefoxStudies": true } }

This example: prevents user extension installs, force-installs uBlock Origin, disables telemetry and updates.

Firefox ESR vs. LibreWolf for Enterprises

LibreWolf is a Firefox fork that ships with privacy-hardened defaults. It's based on Firefox ESR for stability. Some privacy-focused organizations prefer LibreWolf because:

  • No telemetry by default
  • uBlock Origin pre-installed
  • Hardened about:config settings out of the box
  • Community-maintained privacy policy

Trade-off: LibreWolf doesn't have Mozilla's commercial support, enterprise documentation, or Group Policy integration. For strictly enterprise deployments with IT support, Firefox ESR with policies.json is the more manageable choice.

Checking Your Firefox Version (ESR or Rapid?)

about:support → Application Basics → Firefox Edition

Shows either:

  • "Firefox" (Rapid Release)
  • "Firefox Extended Support Release" (ESR)
  • "Firefox Developer Edition" (Developer edition)
  • "Firefox Nightly" (Nightly)

Or check about:config → app.releaseChannel → "esr" for ESR.

Extensions on Firefox ESR

All extensions from AMO work on Firefox ESR. The extension compatibility system works the same way — extensions declare their minimum/maximum Firefox version compatibility in manifest.json.

If you're developing extensions targeting enterprise users on ESR, test on the ESR version to catch issues with Web Extension APIs that were added after the ESR base version.

Security Updates on ESR

ESR receives security updates on the same schedule as rapid release — Mozilla patches critical vulnerabilities in both tracks simultaneously. The security posture of ESR is essentially the same as rapid release; only non-security features are held back.

Critical patches get a .0.1 point release within days of the rapid release security patch.