Bug 1152219 - make reader mode node limit a pref, turn off entirely for desktop because of isProbablyReaderable, r=margaret

modules/libpref/init/all.js

@@ -4672,6 +4672,10 @@ pref("media.gmp-manager.certs.2.commonName", "aus4.mozilla.org");
 // If this pref is disabled, we will never show a reader mode icon in the toolbar.
 pref("reader.parse-on-load.enabled", true);
 
+// After what size document we don't bother running Readability on it
+// because it'd slow things down too much
+pref("reader.parse-node-limit", 3000);
+
 // Force-enables reader mode parsing, even on low-memory platforms, where it
 // is disabled by default.
 pref("reader.parse-on-load.force-enabled", false);