wrapFunctionAndRememberOriginal.js

/**
 * This function will be called before an add-on wraps
 * a `gBrowser` function. A reference to the original
 * function will be saved in `gBrowser.originalFunctions`.
 */
function beforeWrap(gBrowser, fnName) {
  // Ensure that `gBrowser.originalFunctions` exists.
  if (!gBrowser.hasOwnProperty("originalFunctions")) {
    gBrowser.originalFunctions = {};
  }
  
  // Remember the original function, but do not overwrite an
  // already existing reference.
  if (!gBrowser.originalFunctions.hasOwnProperty(fnName)) {
    gBrowser.originalFunctions[fnName] = gBrowser[fnName];
  }
}