The ui.ff file is a plain text file that contains JavaScript or CSS instructions designed to override Firefox’s native user interface (UI). Unlike standard .css files (which handle style), or .js files (which handle behavior), the .ff nomenclature was popularized by third-party tools like and "FxChrome" to denote a "Firefox UI Patch."
The ui.ff file is a plain text file that contains JavaScript or CSS instructions designed to override Firefox’s native user interface (UI). Unlike standard .css files (which handle style), or .js files (which handle behavior), the .ff nomenclature was popularized by third-party tools like and "FxChrome" to denote a "Firefox UI Patch."