Bug 1655014 - use "medium" as default font size, and clear font size when that is used. r=henry

Differential Revision: https://phabricator.services.mozilla.com/D112472

--HG--
extra : rebase_source : 8a8aeb0af5e1a3d3e983586a88a0f1270d1247f1

mail/components/compose/content/MsgComposeCommands.js

@@ -8753,7 +8753,7 @@ function loadHTMLMsgPrefs() {
     doStatefulCommand("cmd_fontFace", fontFace, true);
   }
 
-  let fontSize = Services.prefs.getCharPref("msgcompose.font_size", "");
+  let fontSize = Services.prefs.getCharPref("msgcompose.font_size", "3");
   EditorSetFontSize(fontSize);
 
   let bodyElement = GetBodyElement();

mail/components/compose/content/editor.js

@@ -661,8 +661,23 @@ function onFontFaceChange() {
   fontFaceMenuList.selectedItem = foundFont;
 }
 
+/**
+ * Changes the font size for the selection or at the insertion point. This
+ * requires an integer from 1-7 as a value argument (x-small - xxx-large)
+ *
+ * @param {"1"|"2"|"3"|"4"|"5"|"6"|"7"} size - The font size.
+ */
 function EditorSetFontSize(size) {
-  GetCurrentEditor().document.execCommand("fontSize", false, size);
+  // For normal/medium size (that is 3), we clear size.
+  if (size == "3") {
+    EditorRemoveTextProperty("font", "size");
+    // Also remove big and small,
+    //  else it will seem like size isn't changing correctly
+    EditorRemoveTextProperty("small", "");
+    EditorRemoveTextProperty("big", "");
+  } else {
+    GetCurrentEditor().document.execCommand("fontSize", false, size);
+  }
   // Enable or Disable the toolbar buttons according to the font size.
   goUpdateCommand("cmd_decreaseFontStep");
   goUpdateCommand("cmd_increaseFontStep");

mailnews/mailnews.js

@@ -934,7 +934,7 @@ pref("mailnews.customHeaders", "");
 
 // default msg compose font prefs
 pref("msgcompose.font_face", "");
-pref("msgcompose.font_size", "");
+pref("msgcompose.font_size", "3");
 // If true, let the user agent use default colors (don't set text_color and
 // background_color on the message body).
 pref("msgcompose.default_colors", true);