First draft of popup panel for Firefox Preview

First draft of changes as discussed with Firefox
Preview people.

In order to allow testing/evaluating these changes,
the new advanced setting `uiFlavor` has been added.
Default to `unset`; and can currently only be set
to `fenix`.

The new setting takes effect at launch only. This
new setting is not to be mentioned in official
documentation for now.

This is ongoing work, not open to external feedback.

src/_locales/en/messages.json

@@ -95,6 +95,18 @@
     "message":"or",
     "description":"English: or"
   },
+  "popupBlockedOnThisPage_v2":{
+    "message":"Blocked on this page",
+    "description":"For the new mobile-friendly popup design"
+  },
+  "popupBlockedSinceInstall_v2":{
+    "message":"Blocked since install",
+    "description":"For the new mobile-friendly popup design"
+  },
+  "popupDomainsConnected_v2":{
+    "message":"Domains connected",
+    "description":"For the new mobile-friendly popup design"
+  },
   "popupTipDashboard":{
     "message":"Open the dashboard",
     "description":"English: Click to open the dashboard"
@@ -167,6 +179,26 @@
     "message":"Click to no longer disable JavaScript on this site",
     "description":"Tooltip for the no-scripting per-site switch"
   },
+  "popupNoLargeMedia_v2":{
+    "message":"Large media elements",
+    "description":"Tip for the no-large-media per-site switch"
+  },
+  "popupNoCosmeticFiltering_v2":{
+    "message":"Cosmetic filtering",
+    "description":"Tip for the no-cosmetic-filtering per-site switch"
+  },
+  "popupNoRemoteFonts_v2":{
+    "message":"Remote fonts",
+    "description":"Tip for the no-remote-fonts per-site switch"
+  },
+  "popupNoScripting_v2":{
+    "message":"JavaScript",
+    "description":"Tip for the no-scripting per-site switch"
+  },
+  "popupMoreButton_v2":{
+    "message":"More",
+    "description":"Label to be used to toggle overview panel"
+  },
   "popupTipGlobalRules":{
     "message":"Global rules: this column is for rules which apply to all sites.",
     "description":"Tooltip when hovering the top-most cell of the global-rules column."