SeleniumHQ
diff --git a/‎py/selenium/webdriver/firefox/options.py‎
Lines changed: 12 additions & 0 deletions b/‎py/selenium/webdriver/firefox/options.py‎
Lines changed: 12 additions & 0 deletions
diff --git a/‎py/test/selenium/webdriver/marionette/mn_options_tests.py‎
Lines changed: 21 additions & 0 deletions b/‎py/test/selenium/webdriver/marionette/mn_options_tests.py‎
Lines changed: 21 additions & 0 deletions
diff --git a/‎py/test/selenium/webdriver/marionette/mn_preferences_tests.py‎
Lines changed: 33 additions & 0 deletions b/‎py/test/selenium/webdriver/marionette/mn_preferences_tests.py‎
Lines changed: 33 additions & 0 deletions
@@ -34,6 +34,7 @@ class Options(object):
 
     def __init__(self):
         self._binary = None
+        self._preferences = {}
         self._profile = None
         self._arguments = []
         self.log = Log()
@@ -61,6 +62,15 @@ def binary_location(self):
     def binary_location(self, value):
         self.binary = value
 
+    @property
+    def preferences(self):
+        """Returns a dict of preferences."""
+        return self._preferences
+
+    def set_preference(self, name, value):
+        """Sets a preference."""
+        self._preferences[name] = value
+
     @property
     def profile(self):
         """Returns the Firefox profile to use."""
@@ -100,6 +110,8 @@ def to_capabilities(self):
 
         if self._binary is not None:
             opts["binary"] = self._binary._start_cmd
+        if len(self._preferences) > 0:
+            opts["prefs"] = self._preferences
         if self._profile is not None:
             opts["profile"] = self._profile.encoded
         if len(self._arguments) > 0:
 
@@ -43,6 +43,7 @@ class TestUnit(object):
     def test_ctor(self):
         opts = Options()
         assert opts._binary is None
+        assert opts._preferences == {}
         assert opts._profile is None
         assert opts._arguments == []
         assert isinstance(opts.log, Log)
@@ -61,6 +62,19 @@ def test_binary(self):
         assert isinstance(opts.binary, FirefoxBinary)
         assert opts.binary._start_cmd == path
 
+    def test_prefs(self):
+        opts = Options()
+        assert len(opts.preferences) == 0
+        assert isinstance(opts.preferences, dict)
+
+        opts.set_preference("spam", "ham")
+        assert len(opts.preferences) == 1
+        opts.set_preference("eggs", True)
+        assert len(opts.preferences) == 2
+        opts.set_preference("spam", "spam")
+        assert len(opts.preferences) == 2
+        assert opts.preferences == {"spam": "spam", "eggs": True}
+
     def test_profile(self, tmpdir_factory):
         opts = Options()
         assert opts.profile is None
@@ -108,3 +122,10 @@ def test_to_capabilities(self):
         assert "binary" in caps["moz:firefoxOptions"]
         assert isinstance(caps["moz:firefoxOptions"]["binary"], basestring)
         assert caps["moz:firefoxOptions"]["binary"] == binary._start_cmd
+
+        opts.set_preference("spam", "ham")
+        caps = opts.to_capabilities()
+        assert "moz:firefoxOptions" in caps
+        assert "prefs" in caps["moz:firefoxOptions"]
+        assert isinstance(caps["moz:firefoxOptions"]["prefs"], dict)
+        assert caps["moz:firefoxOptions"]["prefs"]["spam"] == "ham"
@@ -0,0 +1,33 @@
+# Licensed to the Software Freedom Conservancy (SFC) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The SFC licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+import pytest
+
+from selenium.webdriver.firefox.options import Options
+
+
+@pytest.fixture
+def driver_kwargs(request, driver_kwargs):
+    options = Options()
+    options.set_preference('browser.startup.homepage_override.mstone', '')
+    options.set_preference('startup.homepage_welcome_url', 'about:')
+    driver_kwargs['firefox_options'] = options
+    return driver_kwargs
+
+
+def test_preferences_are_used(driver):
+    assert 'about:' == driver.current_url