User-Agent: Mozilla/5.0 (Windows; Windows NT 5.1; rv:2.0b3) Gecko/20100805 Firefox/4.0b3 Build Identifier: Mozilla/5.0 (Windows; Windows NT 5.1; rv:2.0b3) Gecko/20100805 Firefox/4.0b3 In Firefox 4 beta 3 there is a huge input lag when typing to a textarea or textfield on pages with very big dom. Everything is fine when using FireFox 3.6.8. When i type really fast and stop typing, i can see the letters appear after i typed them. Reproducible: Always Steps to Reproduce: 1. Load a page with very big dom 2. Type something fast in textarea or textfield Actual Results: Typed letters appear slowly on screen. Not instantly. Expected Results: Letters should appear instantly.

Can you give an Example or even attach a reduced Testcase?

I created an example. http://mfirm.eu/FF/array-grid.html The easiest way to see the lag is to just type random letters really fast. The lag is much worse than in this example in our real application and is easly seen when typing slowly.

Did you manage to reproduce this bug when opening provided url in FF4.0 Beta3?

Yes, i can reproduce the Issue using Mozilla/5.0 (Windows NT 5.1; rv:2.0b5pre) Gecko/20100819 Minefield/4.0b5pre ID:20100819102200. I fear the Testcase needs to be reduced more and/or at least be profiled (https://wiki.mozilla.org/Performance:Tools). Moreover a Regression-Window (Last Build: ok; First Build: not okay) would help by knowing the "Built from" Url from "about:buildconfig" of these two Builds with checking http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/ ("mozilla-central" flagged Folders).

I did a Regression-Window Last Build OK: Built from http://hg.mozilla.org/mozilla-central/rev/5fda39cd703c downloaded from http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2010/07/ changeset 47677 5fda39cd703c parent 47676 e63da1dc90b6 child 47679 3f5e9b0e02c5 pushlog: 5fda39cd703c First Build not ok: Built from http://hg.mozilla.org/mozilla-central/rev/96de199027d7 downloaded from http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2010/07/2010-07-16-04-mozilla-central/ changeset 47790 96de199027d7 parent 47789 bd21c5390faf child 47791 2d09181ec4cd child 47805 5575b3579d2f

Last Build OK i pasted wrong link. Correct link is: http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2010/07/2010-07-15-04-mozilla-central/

Great! Since that Range points to Bug 564991 as the Cause i verified this by checking saved Hourly Builds before and after Checkin, thus the Range is http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=92339b84d089&tochange=e1d7fd5255fd There are several already filed Performance Regression Bugs, like Bug 579260, Bug 579323, Bug 585258. Without Profiling the Testcase, unsure if already covered by those.

I tested on mozilla 4.0 beta 5 pre and the issue still exists :( Downloaded from: http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2010-08-30-04-mozilla-central/ Version build from: http://hg.mozilla.org/mozilla-central/rev/0487454f4219

Still the same on 4.0b6pre http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2010-09-06-04-mozilla-central/ Built from http://hg.mozilla.org/mozilla-central/rev/67aef7ffb282

I'll investigate this for final but it might be difficult to fix completely.

The reporter's testcase can be loaded at jar:https://bug587439.bugzilla.mozilla.org/attachment.cgi?id=467541!/array-grid.html

** PRODUCT DRIVERS PLEASE NOTE ** This bug is one of 7 automatically changed from blocking2.0:final+ to blocking2.0:.x during the endgame of Firefox 4 for the following reasons: - it was marked as a soft blocking issue without a requirement for beta coverage

Any chance to get it fixed soon?. Out production application is much slower in Firefox4 than it was in Firefox3 in user experience. All user actions like opening new windows, clicking on list boxes, typing etc. are affected by this issue.

Is this still an Issue? If I compare running Attachment 467541 [details] locally against Firefox 3.6, Firefox 4 and Firefox 22/Nightly I believe to see that recent Releases are on par with Firefox 3.6, no?

It ok now.