Changed tags to be lowercase to prevent preprocessing

Changed to have a default for device since it isn't always needed

Tags are more clear

Fixed stylistic issues

lms/djangoapps/courseware/features/login.feature

@@ -12,7 +12,7 @@ Feature: Login in as a registered user
     Then I should see the login error message "This account has not been activated"
 
     # CHROME ONLY, firefox will not redirect properly
-    @Firefox
+    @skip_firefox
     Scenario: Login to an activated account
     Given I am an edX user
     And I am an activated user

lms/djangoapps/courseware/features/signup.feature

@@ -4,7 +4,7 @@ Feature: Sign in
   I want to signup for a student account
 
   # CHROME ONLY, firefox will not redirect properly
-  @Firefox
+  @skip_firefox
   Scenario: Sign up from the homepage
     Given I visit the homepage
     When I click the link with the text "Register Now"

lms/djangoapps/courseware/features/video.feature

@@ -12,7 +12,7 @@ Feature: Video component
   Then when I view the video it has rendered in Youtube mode
 
   #Firefox doesn't have HTML5
-  @Firefox
+  @skip_firefox
   Scenario: Autoplay is enabled in LMS for a Video component
   Given the course has a Video component in HTML5 mode
   Then when I view the video it has autoplay enabled