Firefox must be configured to prevent JavaScript from moving or resizing windows.

JavaScript can make changes to the browser's appearance. This activity can help disguise an attack taking place in a minimized background window. Configure the browser setting to prevent scripts on visited websites from moving and resizing browser windows.

Type "about:policies" in the browser address bar. If "Preferences" is not displayed under Policy Name or the Policy Value does not include "dom.disable_window_move_resize" with a value of "true" and status of "locked", this is a finding.

Windows group policy: 1. Open the group policy editor tool with "gpedit.msc". 2. Navigate to Policy Path: Computer Configuration\Administrative Templates\Mozilla\Firefox\ Policy Name: Preferences Policy State: Enabled Policy Value: { "dom.disable_window_move_resize": { "Value": true, "Status": "locked" } } macOS "plist" file: Add the following: <key>Preferences</key> <dict> <key>dom.disable_window_move_resize</key> <dict> <key>Value</key> <true/> <key>Status</key> <string>locked</string> </dict> </dict> Linux "policies.json" file: Add the following in the policies section: "Preferences": { "dom.disable_window_move_resize": { "Value": true, "Status": "locked" } }