Bug 1740213 - when opening pdf attachments in the 3pane, make sure to put the 3pane in focus. r=henry

Differential Revision: https://phabricator.services.mozilla.com/D130867

--HG--
extra : rebase_source : 5319d819df8aca48c088e91185b66793aaf7c797

mail/base/content/msgHdrView.js

@@ -1937,6 +1937,7 @@ AttachmentInfo.prototype = {
               background: false,
               linkHandler: "single-page",
             });
+            tabmail.ownerDocument.defaultView.focus();
             return;
           }
           // If no tabmail, open PDF same as other attachments.

mail/components/compose/content/MsgComposeCommands.js

@@ -7637,6 +7637,7 @@ function OpenSelectedAttachment() {
           background: false,
           linkHandler: "single-page",
         });
+        tabmail.ownerDocument.defaultView.focus();
         return;
       }
       // If no tabmail, open PDF same as other attachments.