I have a Nexus S startup profile where we restore cnn.com from session. As expected GeckoApp.restoreSessionTabs is called, but it is on the main thread and accounts for 6.6% (~350ms) of startup time. Most of the time is JSONObject.toString (~218ms) but SessionParser.parse is #2 (~96ms) and GeckoProfile.readSessionFile is #3 (~35ms). Since this is all on the main thread it blocks the "next" bit of work, which appears to be starting to load the Gecko libraries. profile: http://people.mozilla.org/~mfinkle/fennec/profiles/nexuss-cnn-startup.trace

One thing I saw when looking at the code. If we are not restoring, we seem to: 1. Read the sessionString 2. Convert the string to a JSON object 3. Convert the JSON to a string 4. Return the string We could probably improve that. http://mxr.mozilla.org/mozilla-central/source/mobile/android/base/GeckoApp.java#1659 http://mxr.mozilla.org/mozilla-central/source/mobile/android/base/GeckoApp.java#1704

We seem to only be calling restoreSessionTabs if we know we need to restore. So comment 1 might be moot. http://mxr.mozilla.org/mozilla-central/source/mobile/android/base/GeckoApp.java#1471 I think we should either fix the issue in comment 1 or remove the mShouldRestore check in restoreSessionTabs.