Since the website was redesigned, I've been noticing very poor performance while typing. I do type reasonably fast, but it's quite noticeable - while typing this, the letters appearing on the screen average at least a couple behind my keystrokes. I see a corresponding CPU usage spike.

The problem presents in:

  • Firefox 3.6.12pre on Ubuntu 10.04
  • Firefox 3.6.6 on CentOS 5.2
  • Konqueror 3.5.4-15 on CentOS 5.2
  • Firefox 3.6.11 on WinXP (assuming this is what daniel means by "fully updated")

But not in:

  • Chrome 7.0.517.41 on Ubuntu 10.04
  • IE 7.0.5730.13 on WinXP (I'm fairly sure - this is on a VM, which lags a little to begin with, but I don't think it's the site)

The Ubuntu 10.04 system has a quad-core Phenom 9950 2.6GHz Radeon HD 4850 (512MB), and the CentOS 5 system has a quad-core 2.66GHz Xeon and a GeForce GTX 280 (1024MB). The lag is more noticeable on the first. These are hardly puny systems. (And I actually have a second Ubuntu 10.04 system - a four-year-old laptop, on which the problem is even worse. I forget the exact specs.)

I would suggest that even if the CPU spike isn't bad enough to cause noticeable lag at your typing speed, it's still evidence the bug is there. Typing probably shouldn't need significant CPU.

(I'll edit this to add more browsers/systems as I can. If anyone can quickly test in Opera or Safari, that might be helpful. I don't have a mac, and I don't have root at work so I can't go off installing more browsers.)

  • me too. I thought it was just my habit of having a dozen (or more) tabs open at once, but apparently not. I only use FF, WinXP, everything fully updated.
    – daniel
    Oct 21, 2010 at 7:09
  • Weird... you should include something about the kind of hardware you've got, I do see a bit of a CPU spike on mine but not enough to actually "lag." Whatever it is has got to be related to the live preview; perhaps Firefox is not very efficient at re-rendering the paper-texture background.
    – Aaronut
    Oct 21, 2010 at 14:07
  • I don't have this problem in ancient FF 1.5 on Linux.
    – justkt
    Oct 22, 2010 at 12:34
  • It's not just live preview, I get the same problem when adding comments. Like this one for example.
    – daniel
    Oct 23, 2010 at 0:45
  • @daniel Thanks for adding that. I forgot to mention it was in comments too. It's actually significantly worse in comments, I think.
    – Cascabel Mod
    Oct 23, 2010 at 1:46

1 Answer 1


OK, I launched Firefox (latest version) and did some typing with task manager in the background.

alt text

I am seeing a spike on 1 out of 4 CPUs during typing. The rest of the CPUs were idle.

Thanks for the detailed testing. Since you said this works in Internet Explorer 7, which is very slow relative to other browsers, this has to be some particular issue with Firefox and this site's CSS.

  • adding a note: I now have to type my comments in a separate program and paste them in. That doesn't seem to present much problem; only when typing live into a text box. The problem also exists when trying to create a new question.
    – daniel
    Oct 25, 2010 at 16:49
  • Interesting note. The site just had me do a captcha, no CPU spike or typing slowdown on that.
    – daniel
    Oct 29, 2010 at 10:13

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