Fixing a bug in as-mac-firefox-get-frontmost-url

Prior to the fix the firefox link grabber won't work correctly if a cursor has been already positioned in the URL field. The fix works by adding an additional keystore for selecting all the text in that field.

contrib/lisp/org-mac-link-grabber.el

@@ -216,8 +216,9 @@ applications and inserting them in org documents"
 					 "	activate\n"
 					 "	delay 0.15\n"
 					 "	tell application \"System Events\"\n"
-					 "		keystroke \"l\" using command down\n"
-					 "		keystroke \"c\" using command down\n"
+					 "		keystroke \"l\" using {command down}\n"
+					 "		keystroke \"a\" using {command down}\n"
+					 "		keystroke \"c\" using {command down}\n"
 					 "	end tell\n"
 					 "	delay 0.15\n"
 					 "	set theUrl to the clipboard\n"