Short bio

PUM.Optional.FirefoxLockedProxy is Malwarebytes’ detection name for a potentially unwanted modification that locks a proxy setting in the Firefox configuration file.

System modifications

In the Firefox configuration file which is usually located at %PROGRAMFILES%\Mozilla Firefox\mozilla.cfg on Windows machines, an entry is found for the network.proxy.type in the lockPref section.


Malwarebytes automatically removes the proxy.type entry to stop triggering the detection of PUM.Optional.FirefoxLockedProxy.

Add an exclusion

When a PUM is detected on your computer, Malwarebytes for Windows does not know if it was authorized. Optimization software, malware, and Potentially Unwanted Programs (PUPs) are known to make these types of changes, hence they are regarded as potentially unwanted.

To have Malwarebytes for Windows ignore a PUM, you must add the PUM as an exclusion.

  1. Open Malwarebytes for Windows.
  2. Click Settings, then click the Protection tab.
  3. Scroll down to the bottom.
  4. Turn off Automatically quarantine detected malware.Turning this setting off prevents Malwarebytes for Windows from quarantining the PUM automatically.
  5. Go to the Dashboard, then click Scan Now.
  6. When the Threat Scan Results appear, uncheck the box next to the detected PUM you want to keep.
  7. Click Next.
  8. On the Remaining Items window, click Ignore Always to add the exclude the detected PUM(s).
  9. Turn on Automatically quarantine detected malware.To find this setting, click Settings > Protection.

When a PUM is excluded, Malwarebytes for Windows does not detect the PUM during scans or Real-Time Protection.

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