Here: http://mxr.mozilla.org/mozilla-central/source/mobile/android/base/widget/LastTabsSection.java#71 We're making a database query per tab to fetch favicons when doing session restore. This is wasteful. Instead we could batch-process the onTabRead events, do a single query, and greatly reduce overheads.
This file has been removed on fig, but it looks like the code still exists in LastTabsPage. Is this a big pain point in practice? I feel like there aren't usually many tabs from last time. Also, now that the UI is different on fig, we should only be doing this when the user actually navigates to the LastTabsPage, so at least it won't affect startup.
We could probably use getFaviconsForUrls() but I'd prefer something like bug 905685.
FYI: my patch for bug 892500 will fix this.