--- a/testing/marionette/element.js
+++ b/testing/marionette/element.js
@@ -233,35 +233,37 @@ element.Store = class {
  *     If <var>strategy</var> is unknown.
  * @throws InvalidSelectorError
  *     If <var>selector</var> is malformed.
  * @throws NoSuchElementError
  *     If a single element is requested, this error will throw if the
  *     element is not found.
  */
 element.find = function(container, strategy, selector, opts = {}) {
-  opts.all = !!opts.all;
-  opts.timeout = opts.timeout || 0;
+  let all = !!opts.all;
+  let timeout = opts.timeout || 0;
+  let startNode = opts.startNode;
 
   let searchFn;
   if (opts.all) {
     searchFn = findElements.bind(this);
   } else {
     searchFn = findElement.bind(this);
   }
 
   return new Promise((resolve, reject) => {
     let findElements = new PollPromise((resolve, reject) => {
-      let res = find_(container, strategy, selector, searchFn, opts);
+      let res = find_(container, strategy, selector, searchFn,
+          {all, startNode});
       if (res.length > 0) {
         resolve(Array.from(res));
       } else {
         reject([]);
       }
-    }, opts.timeout);
+    }, {timeout});
 
     findElements.then(foundEls => {
       // the following code ought to be moved into findElement
       // and findElements when bug 1254486 is addressed
       if (!opts.all && (!foundEls || foundEls.length == 0)) {
         let msg;
         switch (strategy) {
           case element.Strategy.AnonAttribute:
@@ -279,23 +281,21 @@ element.find = function(container, strat
       if (opts.all) {
         resolve(foundEls);
       }
       resolve(foundEls[0]);
     }, reject);
   });
 };
 
-function find_(container, strategy, selector, searchFn, opts) {
+function find_(container, strategy, selector, searchFn,
+    {startNode = null, all = false} = {}) {
   let rootNode = container.shadowRoot || container.frame.document;
-  let startNode;
 
-  if (opts.startNode) {
-    startNode = opts.startNode;
-  } else {
+  if (!startNode) {
     switch (strategy) {
       // For anonymous nodes the start node needs to be of type
       // DOMElement, which will refer to :root in case of a DOMDocument.
       case element.Strategy.Anon:
       case element.Strategy.AnonAttribute:
         if (rootNode instanceof Ci.nsIDOMDocument) {
           startNode = rootNode.documentElement;
         }
@@ -310,17 +310,17 @@ function find_(container, strategy, sele
   try {
     res = searchFn(strategy, selector, rootNode, startNode);
   } catch (e) {
     throw new InvalidSelectorError(
         `Given ${strategy} expression "${selector}" is invalid: ${e}`);
   }
 
   if (res) {
-    if (opts.all) {
+    if (all) {
       return res;
     }
     return [res];
   }
   return [];
 }
 
 /**

--- a/testing/marionette/sync.js
+++ b/testing/marionette/sync.js
@@ -77,17 +77,17 @@ const {TYPE_ONE_SHOT, TYPE_REPEATING_SLA
  *
  * @return {Promise.<*>}
  *     Yields the value passed to <var>func</var>'s
  *     <code>resolve</code> or <code>reject</code> callbacks.
  *
  * @throws {*}
  *     If <var>func</var> throws, its error is propagated.
  */
-function PollPromise(func, timeout = 2000, interval = 10) {
+function PollPromise(func, {timeout = 2000, interval = 10} = {}) {
   const timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
 
   return new Promise((resolve, reject) => {
     const start = new Date().getTime();
     const end = start + timeout;
 
     let evalFn = () => {
       new Promise(func).then(resolve, rejected => {

--- a/testing/marionette/test_sync.js
+++ b/testing/marionette/test_sync.js
@@ -43,34 +43,34 @@ add_task(async function test_PollPromise
 
 add_task(async function test_PollPromise_noTimeout() {
   // run at least once when timeout is 0
   let nevals = 0;
   let start = new Date().getTime();
   await new PollPromise((resolve, reject) => {
     ++nevals;
     reject();
-  }, 0);
+  }, {timeout: 0});
   let end = new Date().getTime();
   equal(1, nevals);
   less((end - start), DEFAULT_TIMEOUT);
 });
 
 add_task(async function test_PollPromise_timeout() {
   let nevals = 0;
   let start = new Date().getTime();
   await new PollPromise((resolve, reject) => {
     ++nevals;
     reject();
-  }, 100);
+  }, {timeout: 100});
   let end = new Date().getTime();
   greater(nevals, 1);
   greaterOrEqual((end - start), 100);
 });
 
 add_task(async function test_PollPromise_interval() {
   let nevals = 0;
   await new PollPromise((resolve, reject) => {
     ++nevals;
     reject();
-  }, 100, 100);
+  }, {timeout: 100, interval: 100});
   equal(2, nevals);
 });