Add browser features around virtual/accessibility focus

These would help in making hidden skip links show up visually once they
receive AT focus (for sighted/partially sighted AT users)

docs/_data/browser-features.yml

@@ -1,3 +1,23 @@
+-
+  browser: >
+    Edge
+  summary: >
+    Focusable elements should fire focus event / receive :focus styling when they receive Narrator/accessibility focus
+  upstream_bug: >
+    UserVoice#16717318
+  origin: >
+    Bootstrap#20732
+
+-
+  browser: >
+    Firefox
+  summary: >
+    When virtual focus is on a button or link, fire actual focus on the element, too
+  upstream_bug: >
+    Mozilla#1000082
+  origin: >
+    Bootstrap#20732
+    
 -
   browser: >
     Edge