added nightly support for alpha & colorspace

Author: dletorey

html/elements/input.json

@@ -148,7 +148,7 @@
               "chrome_android": "mirror",
               "edge": "mirror",
               "firefox": {
-                "version_added": false,
+                "version_added": "preview",
                 "impl_url": "https://bugzil.la/1919718"
               },
               "firefox_android": "mirror",
@@ -355,7 +355,7 @@
               "chrome_android": "mirror",
               "edge": "mirror",
               "firefox": {
-                "version_added": false,
+                "version_added": "preview",
                 "impl_url": "https://bugzil.la/1919718"
               },
               "firefox_android": "mirror",