Control use of the Web Serial API
Verified with Mozilla Firefox v8.2 — updated on July 10, 2026
Supported on: Firefox 151 or later
Path in the GPO console
Computer Configuration\Administrative Templates\Mozilla\Firefox User Configuration\Administrative Templates\Mozilla\Firefox Description
If this policy is enabled, you can control whether websites can request access to serial ports. Note: If any other policies are configured and this policy is not set, the Web Serial API is blocked by default.
Registry
HKLM
Software\Policies\Mozilla\Firefox HKCU
Software\Policies\Mozilla\Firefox Export Builder
BETAConfigure the state, scope and options, then generate .reg, PowerShell, Intune and SCCM outputs — or add the setting to a multi-setting collection.
These exports write the registry — this is not a managed GPO. ⓘ
Applying both scopes creates an ambiguous configuration (computer takes precedence over user). Only do this intentionally.
.reg file
Windows Registry Editor Version 5.00
; Exported from gporais.com
; Policy: Control use of the Web Serial API
; State: Enabled
; Scope: Computer (HKLM)
; Supported on: Firefox 151 or later
[HKEY_LOCAL_MACHINE\Software\Policies\Mozilla\Firefox]
"DefaultSerialGuardSetting"=dword:00000002More formats (PowerShell, Intune, SCCM)
PowerShell
# Exported from gporais.com
# Policy: Control use of the Web Serial API
# State: Enabled
# Scope: Computer (HKLM)
# Supported on: Firefox 151 or later
$path = 'HKLM:\Software\Policies\Mozilla\Firefox'
New-Item -Path $path -Force | Out-Null
Set-ItemProperty -Path $path -Name 'DefaultSerialGuardSetting' -Value 2 -Type DWordIntune XML
No direct Policy CSP / OMA-URI mapping for this policy. Use the Intune Remediation tab, or ingest the ADMX in Intune.Intune Remediation
# === Detection script ===
# Exported from gporais.com
# Policy: Control use of the Web Serial API
# State: Enabled
# Scope: Computer (HKLM)
# Supported on: Firefox 151 or later
function Test-RegistryValue {
param(
[Parameter(Mandatory = $true)][string]$Path,
[Parameter(Mandatory = $true)][string]$Name,
[object]$Expected,
[ValidateSet('String', 'DWord', 'MultiString')][string]$Kind = 'String',
[switch]$Absent
)
try {
$item = Get-ItemProperty -LiteralPath $Path -Name $Name -ErrorAction Stop
} catch {
return $Absent.IsPresent
}
if ($Absent.IsPresent) { return $false }
$actual = $item.$Name
if ($Kind -eq 'DWord') { return ([int64]$actual) -eq ([int64]$Expected) }
if ($Kind -eq 'MultiString') {
$actualValues = @($actual)
$expectedValues = @($Expected)
if ($actualValues.Count -ne $expectedValues.Count) { return $false }
for ($i = 0; $i -lt $expectedValues.Count; $i++) {
if ([string]$actualValues[$i] -ne [string]$expectedValues[$i]) { return $false }
}
return $true
}
return [string]$actual -eq [string]$Expected
}
$checks = @(
(Test-RegistryValue -Path 'HKLM:\Software\Policies\Mozilla\Firefox' -Name 'DefaultSerialGuardSetting' -Expected 2 -Kind DWord)
)
if ($checks -notcontains $false) {
Write-Output 'Compliant'
exit 0
}
Write-Output 'Non-compliant'
exit 1
# === Remediation script ===
# Exported from gporais.com
# Policy: Control use of the Web Serial API
# State: Enabled
# Scope: Computer (HKLM)
# Supported on: Firefox 151 or later
$path = 'HKLM:\Software\Policies\Mozilla\Firefox'
New-Item -Path $path -Force | Out-Null
Set-ItemProperty -Path $path -Name 'DefaultSerialGuardSetting' -Value 2 -Type DWordSCCM scripts
# Exported from gporais.com
# Policy: Control use of the Web Serial API
# State: Enabled
# Scope: Computer (HKLM)
# Supported on: Firefox 151 or later
# SCCM Configuration Item guidance:
# Create a Configuration Item of type "Setting: Script".
# Discovery script: use the Detection script below.
# Remediation script: use the Remediation script below.
# Compliance rule: the Discovery script output equals 'Compliant'.
# === Detection script ===
# Exported from gporais.com
# Policy: Control use of the Web Serial API
# State: Enabled
# Scope: Computer (HKLM)
# Supported on: Firefox 151 or later
function Test-RegistryValue {
param(
[Parameter(Mandatory = $true)][string]$Path,
[Parameter(Mandatory = $true)][string]$Name,
[object]$Expected,
[ValidateSet('String', 'DWord', 'MultiString')][string]$Kind = 'String',
[switch]$Absent
)
try {
$item = Get-ItemProperty -LiteralPath $Path -Name $Name -ErrorAction Stop
} catch {
return $Absent.IsPresent
}
if ($Absent.IsPresent) { return $false }
$actual = $item.$Name
if ($Kind -eq 'DWord') { return ([int64]$actual) -eq ([int64]$Expected) }
if ($Kind -eq 'MultiString') {
$actualValues = @($actual)
$expectedValues = @($Expected)
if ($actualValues.Count -ne $expectedValues.Count) { return $false }
for ($i = 0; $i -lt $expectedValues.Count; $i++) {
if ([string]$actualValues[$i] -ne [string]$expectedValues[$i]) { return $false }
}
return $true
}
return [string]$actual -eq [string]$Expected
}
$checks = @(
(Test-RegistryValue -Path 'HKLM:\Software\Policies\Mozilla\Firefox' -Name 'DefaultSerialGuardSetting' -Expected 2 -Kind DWord)
)
if ($checks -notcontains $false) {
Write-Output 'Compliant'
exit 0
}
Write-Output 'Non-compliant'
exit 1
# === Remediation script ===
# Exported from gporais.com
# Policy: Control use of the Web Serial API
# State: Enabled
# Scope: Computer (HKLM)
# Supported on: Firefox 151 or later
$path = 'HKLM:\Software\Policies\Mozilla\Firefox'
New-Item -Path $path -Force | Out-Null
Set-ItemProperty -Path $path -Name 'DefaultSerialGuardSetting' -Value 2 -Type DWordBuilding a multi-setting collection? Add this setting and generate combined .reg / PowerShell / GPO scripts.