If we call gBrowser.addTab(); then in the method addTab var blank = (aURI == "about:blank") is false if also for cases that aURI is null or undefined. The result is unnecessary call to loadURIWithFlags, and that slowdown the process of opening new tabs, especially when we open many tabs at once. For example nsSessionStore first add new tabs with addTab() and just after that it call to restore tab history. One solution is to replace everywhere addTab() with addTab("about:blank") or to replace in gBrowser.addTab: - var blank = (aURI == "about:blank"); - var blank = (aURI != null) ? (aURI == "about:blank") : true;

For the reference: http://mxr.mozilla.org/mozilla-central/source/browser/base/content/tabbrowser.xml#1203 1203 var blank = (aURI == "about:blank"); http://mxr.mozilla.org/mozilla-central/search?string=.addTab%28%29&find=&findi=&filter=^[^\0]*%24&hitlimit=&tree=mozilla-central

I fixed this in bug 320989, but it might be a good idea to do this independently.

Comment on attachment 405665 [details] [diff] [review] patch r=mano

Tests have been updated. So I assume those would cover any regression. Marking verified fixed based on no broken tests.

Comment on attachment 405665 [details] [diff] [review] patch "approval1.9.2.1=?": No risk, little perf win.

Comment on attachment 405665 [details] [diff] [review] patch No risk, small perf win, 1.9.2.3+

Comment on attachment 405665 [details] [diff] [review] patch Sorry for the bugspam - this should have been moved to a ?, not a +. I think we should take this in 1.9.2.3, but the tree isn't yet open for those checkins, so we'll circle back around and + once it is.

Comment on attachment 405665 [details] [diff] [review] patch Approved for 1.9.2.3, a=dveditz for release-drivers not approved for 1.9.1, a minor perf win isn't worth it.

Backed out because it was triggering an orange in browser_keyevents_during_autoscrolling.js. (I get the same failures when I run that test directly even without the patch, so I suspect it's an underlying issue with the test that this just further exposed.)

Comment on attachment 405665 [details] [diff] [review] patch Missed the 1.9.2.4 release, removing approval.