--- a/testing/marionette/driver.js
+++ b/testing/marionette/driver.js
@@ -151,24 +151,24 @@ this.GeckoDriver = function (appName, se
     // mandated capabilities
     "browserName": Services.appinfo.name.toLowerCase(),
     "browserVersion": Services.appinfo.version,
     "platformName": Services.sysinfo.getProperty("name").toLowerCase(),
     "platformVersion": Services.sysinfo.getProperty("version"),
     "acceptInsecureCerts": !this.secureTLS,
 
     // supported features
-    "raisesAccessibilityExceptions": false,
     "rotatable": this.appName == "B2G",
     "proxy": {},
 
     // proprietary extensions
     "specificationLevel": 0,
     "moz:processID": Services.appinfo.processID,
     "moz:profile": Services.dirsvc.get("ProfD", Ci.nsIFile).path,
+    "moz:accessibilityChecks": false,
   };
 
   this.mm = globalMessageManager;
   this.listener = proxy.toListener(() => this.mm, this.sendAsync.bind(this));
 
   // always keep weak reference to current dialogue
   this.dialog = null;
   let handleDialog = (subject, topic) => {
@@ -178,16 +178,20 @@ this.GeckoDriver = function (appName, se
     }
     this.dialog = new modal.Dialog(() => this.curBrowser, winr);
   };
   modal.addHandler(handleDialog);
 
   this.actions = new action.Chain();
 };
 
+Object.defineProperty(GeckoDriver.prototype, "a11yChecks", {
+  get: function () { return this.sessionCapabilities["moz:accessibilityChecks"]; }
+});
+
 GeckoDriver.prototype.QueryInterface = XPCOMUtils.generateQI([
   Ci.nsIMessageListener,
   Ci.nsIObserver,
   Ci.nsISupportsWeakReference
 ]);
 
 /**
  * Switches to the global ChromeMessageBroadcaster, potentially replacing
@@ -514,18 +518,17 @@ GeckoDriver.prototype.newSession = funct
     logger.warn("TLS certificate errors will be ignored for this session");
     let acceptAllCerts = new cert.InsecureSweepingOverride();
     cert.installOverride(acceptAllCerts);
   }
 
   // If we are testing accessibility with marionette, start a11y service in
   // chrome first. This will ensure that we do not have any content-only
   // services hanging around.
-  if (this.sessionCapabilities.raisesAccessibilityExceptions &&
-      accessibility.service) {
+  if (this.a11yChecks && accessibility.service) {
     logger.info("Preemptively starting accessibility service in Chrome");
   }
 
   let registerBrowsers = this.registerPromise();
   let browserListening = this.listeningPromise();
 
   let waitForWindow = function() {
     let win = this.getCurrentWindow();
@@ -1800,18 +1803,17 @@ GeckoDriver.prototype.getActiveElement =
  */
 GeckoDriver.prototype.clickElement = function*(cmd, resp) {
   let id = cmd.parameters.id;
 
   switch (this.context) {
     case Context.CHROME:
       let win = this.getCurrentWindow();
       let el = this.curBrowser.seenEls.get(id, {frame: win});
-      yield interaction.clickElement(
-          el, this.sessionCapabilities.raisesAccessibilityExceptions);
+      yield interaction.clickElement(el, this.a11yChecks);
       break;
 
     case Context.CONTENT:
       // We need to protect against the click causing an OOP frame to close.
       // This fires the mozbrowserclose event when it closes so we need to
       // listen for it and then just send an error back. The person making the
       // call should be aware something isnt right and handle accordingly
       this.addFrameCloseListener("click");
@@ -1931,17 +1933,17 @@ GeckoDriver.prototype.getElementTagName 
 GeckoDriver.prototype.isElementDisplayed = function*(cmd, resp) {
   let id = cmd.parameters.id;
 
   switch (this.context) {
     case Context.CHROME:
       let win = this.getCurrentWindow();
       let el = this.curBrowser.seenEls.get(id, {frame: win});
       resp.body.value = yield interaction.isElementDisplayed(
-          el, this.sessionCapabilities.raisesAccessibilityExceptions);
+          el, this.a11yChecks);
       break;
 
     case Context.CONTENT:
       resp.body.value = yield this.listener.isElementDisplayed(id);
       break;
   }
 };
 
@@ -1980,17 +1982,17 @@ GeckoDriver.prototype.isElementEnabled =
   let id = cmd.parameters.id;
 
   switch (this.context) {
     case Context.CHROME:
       // Selenium atom doesn't quite work here
       let win = this.getCurrentWindow();
       let el = this.curBrowser.seenEls.get(id, {frame: win});
       resp.body.value = yield interaction.isElementEnabled(
-          el, this.sessionCapabilities.raisesAccessibilityExceptions);
+          el, this.a11yChecks);
       break;
 
     case Context.CONTENT:
       resp.body.value = yield this.listener.isElementEnabled(id);
       break;
   }
 },
 
@@ -2004,17 +2006,17 @@ GeckoDriver.prototype.isElementSelected 
   let id = cmd.parameters.id;
 
   switch (this.context) {
     case Context.CHROME:
       // Selenium atom doesn't quite work here
       let win = this.getCurrentWindow();
       let el = this.curBrowser.seenEls.get(id, {frame: win});
       resp.body.value = yield interaction.isElementSelected(
-          el, this.sessionCapabilities.raisesAccessibilityExceptions);
+          el, this.a11yChecks);
       break;
 
     case Context.CONTENT:
       resp.body.value = yield this.listener.isElementSelected(id);
       break;
   }
 };
 
@@ -2052,17 +2054,17 @@ GeckoDriver.prototype.sendKeysToElement 
   let {id, value} = cmd.parameters;
   assert.defined(value, `Expected character sequence: ${value}`);
 
   switch (this.context) {
     case Context.CHROME:
       let win = this.getCurrentWindow();
       let el = this.curBrowser.seenEls.get(id, {frame: win});
       yield interaction.sendKeysToElement(
-          el, value, true, this.sessionCapabilities.raisesAccessibilityExceptions);
+          el, value, true, this.a11yChecks);
       break;
 
     case Context.CONTENT:
       yield this.listener.sendKeysToElement(id, value);
       break;
   }
 };
 

--- a/testing/marionette/harness/marionette_harness/tests/unit/test_accessibility.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_accessibility.py
@@ -85,20 +85,19 @@ class TestAccessibility(MarionetteTestCa
     # Elements that are reporting selected state
     valid_option_elementIDs = ["option1", "option2"]
 
     def run_element_test(self, ids, testFn):
         for id in ids:
             element = self.marionette.find_element(By.ID, id)
             testFn(element)
 
-    def setup_accessibility(self, raisesAccessibilityExceptions=True, navigate=True):
+    def setup_accessibility(self, enable_a11y_checks=True, navigate=True):
         self.marionette.delete_session()
-        self.marionette.start_session(
-            {"raisesAccessibilityExceptions": raisesAccessibilityExceptions})
+        self.marionette.start_session({"moz:accessibilityChecks": enable_a11y_checks})
         # Navigate to test_accessibility.html
         if navigate:
             test_accessibility = self.marionette.absolute_url("test_accessibility.html")
             self.marionette.navigate(test_accessibility)
 
     def test_valid_single_tap(self):
         self.setup_accessibility()
         # No exception should be raised

--- a/testing/marionette/harness/marionette_harness/tests/unit/test_capabilities.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_capabilities.py
@@ -43,16 +43,19 @@ class TestCapabilities(MarionetteTestCas
         self.assertEqual(self.caps["moz:processID"], self.appinfo["processID"])
         self.assertEqual(self.marionette.process_id, self.appinfo["processID"])
 
         current_profile = self.marionette.instance.runner.profile.profile
         self.assertIn("moz:profile", self.caps)
         self.assertEqual(self.caps["moz:profile"], current_profile)
         self.assertEqual(self.marionette.profile, current_profile)
 
+        self.assertIn("moz:accessibilityChecks", self.caps)
+        self.assertFalse(self.caps["moz:accessibilityChecks"])
+
     def test_we_can_pass_in_capabilities_on_session_start(self):
         self.marionette.delete_session()
         capabilities = {"desiredCapabilities": {"somethingAwesome": "cake"}}
         self.marionette.start_session(capabilities)
         caps = self.marionette.session_capabilities
         self.assertIn("somethingAwesome", caps)
 
     def test_set_specification_level(self):

--- a/testing/marionette/listener.js
+++ b/testing/marionette/listener.js
@@ -630,17 +630,17 @@ function emitTouchEvent(type, touch) {
 function singleTap(id, corx, cory) {
   let el = seenEls.get(id, curContainer);
   // after this block, the element will be scrolled into view
   let visible = element.isVisible(el, corx, cory);
   if (!visible) {
     throw new ElementNotVisibleError("Element is not currently visible and may not be manipulated");
   }
 
-  let a11y = accessibility.get(capabilities.raisesAccessibilityExceptions);
+  let a11y = accessibility.get(capabilities["moz:accessibilityChecks"]);
   return a11y.getAccessible(el, true).then(acc => {
     a11y.assertVisible(acc, el, visible);
     a11y.assertActionable(acc, el);
     if (!curContainer.frame.document.createTouch) {
       actions.mouseEventsOnly = true;
     }
     let c = element.coordinates(el, corx, cory);
     if (!actions.mouseEventsOnly) {
@@ -1153,17 +1153,17 @@ function getActiveElement() {
  *
  * @param {WebElement} id
  *     Reference to the web element to click.
  */
 function clickElement(id) {
   let el = seenEls.get(id, curContainer);
   return interaction.clickElement(
       el,
-      !!capabilities.raisesAccessibilityExceptions,
+      !!capabilities["moz:accessibilityChecks"],
       capabilities.specificationLevel >= 1);
 }
 
 function getElementAttribute(id, name) {
   let el = seenEls.get(id, curContainer);
   if (element.isBooleanAttribute(el, name)) {
     if (el.hasAttribute(name)) {
       return "true";
@@ -1212,17 +1212,17 @@ function getElementTagName(id) {
  * Determine the element displayedness of the given web element.
  *
  * Also performs additional accessibility checks if enabled by session
  * capability.
  */
 function isElementDisplayed(id) {
   let el = seenEls.get(id, curContainer);
   return interaction.isElementDisplayed(
-      el, capabilities.raisesAccessibilityExceptions);
+      el, capabilities["moz:accessibilityChecks"]);
 }
 
 /**
  * Retrieves the computed value of the given CSS property of the given
  * web element.
  *
  * @param {String} id
  *     Web element reference.
@@ -1265,39 +1265,39 @@ function getElementRect(id) {
  *     Reference to web element.
  *
  * @return {boolean}
  *     True if enabled, false otherwise.
  */
 function isElementEnabled(id) {
   let el = seenEls.get(id, curContainer);
   return interaction.isElementEnabled(
-      el, capabilities.raisesAccessibilityExceptions);
+      el, capabilities["moz:accessibilityChecks"]);
 }
 
 /**
  * Determines if the referenced element is selected or not.
  *
  * This operation only makes sense on input elements of the Checkbox-
  * and Radio Button states, or option elements.
  */
 function isElementSelected(id) {
   let el = seenEls.get(id, curContainer);
   return interaction.isElementSelected(
-      el, capabilities.raisesAccessibilityExceptions);
+      el, capabilities["moz:accessibilityChecks"]);
 }
 
 function* sendKeysToElement(id, val) {
   let el = seenEls.get(id, curContainer);
   if (el.type == "file") {
     let path = val.join("");
     yield interaction.uploadFile(el, path);
   } else {
     yield interaction.sendKeysToElement(
-        el, val, false, capabilities.raisesAccessibilityExceptions);
+        el, val, false, capabilities["moz:accessibilityChecks"]);
   }
 }
 
 /**
  * Clear the text of an element.
  */
 function clearElement(id) {
   try {