--- a/browser/extensions/formautofill/FormAutofillContent.jsm
+++ b/browser/extensions/formautofill/FormAutofillContent.jsm
@@ -93,17 +93,17 @@ AutofillProfileAutoCompleteSearch.protot
    * @param {string} searchParam
    * @param {Object} previousResult a previous result to use for faster searchinig
    * @param {Object} listener the listener to notify when the search is complete
    */
   startSearch(searchString, searchParam, previousResult, listener) {
     let {activeInput, activeSection, activeFieldDetail, savedFieldNames} = FormAutofillContent;
     this.forceStop = false;
 
-    this.log.debug("startSearch: for", searchString, "with input", activeInput);
+    this.debug("startSearch: for", searchString, "with input", activeInput);
 
     let isAddressField = FormAutofillUtils.isAddressField(activeFieldDetail.fieldName);
     let isInputAutofilled = activeFieldDetail.state == FIELD_STATES.AUTO_FILLED;
     let allFieldNames = activeSection.allFieldNames;
     let filledRecordGUID = activeSection.filledRecordGUID;
     let searchPermitted = isAddressField ?
                           FormAutofillUtils.isAutofillAddressesEnabled :
                           FormAutofillUtils.isAutofillCreditCardsEnabled;
@@ -191,17 +191,17 @@ AutofillProfileAutoCompleteSearch.protot
    * @param  {string} data.searchString
    *         The typed string for filtering out the matched records.
    * @param  {string} data.info
    *         The input autocomplete property's information.
    * @returns {Promise}
    *          Promise that resolves when addresses returned from parent process.
    */
   _getRecords(data) {
-    this.log.debug("_getRecords with data:", data);
+    this.debug("_getRecords with data:", data);
     return new Promise((resolve) => {
       Services.cpmm.addMessageListener("FormAutofill:Records", function getResult(result) {
         Services.cpmm.removeMessageListener("FormAutofill:Records", getResult);
         resolve(result.data);
       });
 
       Services.cpmm.sendAsyncMessage("FormAutofill:GetRecords", data);
     });
@@ -217,30 +217,30 @@ let ProfileAutocomplete = {
   _factory: null,
 
   ensureRegistered() {
     if (this._registered) {
       return;
     }
 
     FormAutofillUtils.defineLazyLogGetter(this, "ProfileAutocomplete");
-    this.log.debug("ensureRegistered");
+    this.debug("ensureRegistered");
     this._factory = new AutocompleteFactory();
     this._factory.register(AutofillProfileAutoCompleteSearch);
     this._registered = true;
 
     Services.obs.addObserver(this, "autocomplete-will-enter-text");
   },
 
   ensureUnregistered() {
     if (!this._registered) {
       return;
     }
 
-    this.log.debug("ensureUnregistered");
+    this.debug("ensureUnregistered");
     this._factory.unregister();
     this._factory = null;
     this._registered = false;
     this._lastAutoCompleteResult = null;
 
     Services.obs.removeObserver(this, "autocomplete-will-enter-text");
   },
 
@@ -270,17 +270,17 @@ let ProfileAutocomplete = {
     if (selectedIndexResult.length != 1 || !Number.isInteger(selectedIndexResult[0])) {
       throw new Error("Invalid autocomplete selectedIndex");
     }
 
     return selectedIndexResult[0];
   },
 
   _fillFromAutocompleteRow(focusedInput) {
-    this.log.debug("_fillFromAutocompleteRow:", focusedInput);
+    this.debug("_fillFromAutocompleteRow:", focusedInput);
     let formDetails = FormAutofillContent.activeFormDetails;
     if (!formDetails) {
       // The observer notification is for a different frame.
       return;
     }
 
     let selectedIndex = this._getSelectedIndex(focusedInput.ownerGlobal);
     if (selectedIndex == -1 ||
@@ -383,31 +383,31 @@ var FormAutofillContent = {
    * 3. Number of filled fields is less than autofill threshold
    *
    * @param {HTMLElement} formElement Root element which receives earlyformsubmit event.
    * @param {Object} domWin Content window
    * @returns {boolean} Should always return true so form submission isn't canceled.
    */
   notify(formElement, domWin) {
     try {
-      this.log.debug("Notifying form early submission");
+      this.debug("Notifying form early submission");
 
       if (!FormAutofillUtils.isAutofillEnabled) {
-        this.log.debug("Form Autofill is disabled");
+        this.debug("Form Autofill is disabled");
         return true;
       }
 
       if (domWin && PrivateBrowsingUtils.isContentWindowPrivate(domWin)) {
-        this.log.debug("Ignoring submission in a private window");
+        this.debug("Ignoring submission in a private window");
         return true;
       }
 
       let handler = this._formsDetails.get(formElement);
       if (!handler) {
-        this.log.debug("Form element could not map to an existing handler");
+        this.debug("Form element could not map to an existing handler");
         return true;
       }
 
       let records = handler.createRecords();
       if (!Object.values(records).some(typeRecords => typeRecords.length)) {
         return true;
       }
 
@@ -525,36 +525,36 @@ var FormAutofillContent = {
           break;
         }
       }
     }
     return this._activeItems.fieldDetail;
   },
 
   identifyAutofillFields(element) {
-    this.log.debug("identifyAutofillFields:", "" + element.ownerDocument.location);
+    this.debug("identifyAutofillFields:", element.ownerDocument.location.href);
 
     if (!this.savedFieldNames) {
-      this.log.debug("identifyAutofillFields: savedFieldNames are not known yet");
+      this.debug("identifyAutofillFields: savedFieldNames are not known yet");
       Services.cpmm.sendAsyncMessage("FormAutofill:InitStorage");
     }
 
     let formHandler = this._getFormHandler(element);
     if (!formHandler) {
       let formLike = FormLikeFactory.createFromField(element);
       formHandler = new FormAutofillHandler(formLike);
     } else if (!formHandler.updateFormIfNeeded(element)) {
-      this.log.debug("No control is removed or inserted since last collection.");
+      this.debug("No control is removed or inserted since last collection.");
       return;
     }
 
     let validDetails = formHandler.collectFormFields();
 
     this._formsDetails.set(formHandler.form.rootElement, formHandler);
-    this.log.debug("Adding form handler to _formsDetails:", formHandler);
+    this.debug("Adding form handler to _formsDetails:", formHandler);
 
     validDetails.forEach(detail =>
       this._markAsAutofillField(detail.elementWeakRef.get())
     );
   },
 
   clearForm() {
     let focusedInput = this.activeInput || ProfileAutocomplete._lastAutoCompleteFocusedInput;

--- a/browser/extensions/formautofill/FormAutofillUtils.jsm
+++ b/browser/extensions/formautofill/FormAutofillUtils.jsm
@@ -40,16 +40,36 @@ const SECTION_TYPES = {
 // attacks that fill the user's hard drive(s).
 const MAX_FIELD_VALUE_LENGTH = 200;
 
 ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 ChromeUtils.import("resource://gre/modules/Services.jsm");
 ChromeUtils.defineModuleGetter(this, "CreditCard",
   "resource://gre/modules/CreditCard.jsm");
 
+XPCOMUtils.defineLazyPreferenceGetter(this, "logLevel", "extensions.formautofill.loglevel",
+                                      "error");
+
+// A logging helper for debug logging to avoid creating Console objects
+// or triggering expensive JS -> C++ calls when debug logging is not
+// enabled.
+//
+// Console objects, even natively-implemented ones, can consume a lot of
+// memory, and since this code may run in every content process, that
+// memory can add up quickly. And, even when debug-level messages are
+// being ignored, console.debug() calls can be expensive.
+//
+// This helper avoids both of those problems by never touching the
+// console object unless debug logging is enabled.
+function debug() {
+  if (logLevel == "debug") {
+    this.log.debug(...arguments);
+  }
+}
+
 let AddressDataLoader = {
   // Status of address data loading. We'll load all the countries with basic level 1
   // information while requesting conutry information, and set country to true.
   // Level 1 Set is for recording which country's level 1/level 2 data is loaded,
   // since we only load this when getCountryAddressData called with level 1 parameter.
   _dataLoaded: {
     country: false,
     level1: new Set(),
@@ -333,16 +353,18 @@ this.FormAutofillUtils = {
     for (let field in address) {
       if (field != "tel" && this.getCategoryFromFieldName(field) == "tel") {
         delete address[field];
       }
     }
   },
 
   defineLazyLogGetter(scope, logPrefix) {
+    scope.debug = debug;
+
     XPCOMUtils.defineLazyGetter(scope, "log", () => {
       let ConsoleAPI = ChromeUtils.import("resource://gre/modules/Console.jsm", {}).ConsoleAPI;
       return new ConsoleAPI({
         maxLogLevelPref: "extensions.formautofill.loglevel",
         prefix: logPrefix,
       });
     });
   },