diff --git a/rb/lib/selenium/webdriver/firefox/options.rb b/rb/lib/selenium/webdriver/firefox/options.rb
index d65966611cd00..80b08a017eed9 100644
--- a/rb/lib/selenium/webdriver/firefox/options.rb
+++ b/rb/lib/selenium/webdriver/firefox/options.rb
@@ -175,7 +175,7 @@ def process_profile(profile)
         end
 
         def camelize?(key)
-          key != :prefs
+          key != "prefs"
         end
       end # Options
     end # Firefox
diff --git a/rb/spec/unit/selenium/webdriver/firefox/options_spec.rb b/rb/spec/unit/selenium/webdriver/firefox/options_spec.rb
index 991cf46691d90..cc3a95e1a9fc9 100644
--- a/rb/spec/unit/selenium/webdriver/firefox/options_spec.rb
+++ b/rb/spec/unit/selenium/webdriver/firefox/options_spec.rb
@@ -149,6 +149,14 @@ module Firefox
             options.add_preference(:foo, 'bar')
             expect(options.prefs[:foo]).to eq('bar')
           end
+
+          it 'does not camelize preferences' do
+            options.add_preference('intl.accepted_languages', 'en-US')
+
+            prefs    = options.as_json['moz:firefoxOptions']['prefs']
+            expected = { 'intl.accepted_languages' => 'en-US' }
+            expect(prefs).to eq(expected)
+          end
         end
 
         describe '#enable_android' do