Speed up that sluggish Iceweasel/Firefox
For quite some time I have wondered why Iceweasel on my Debian Squeeze systems was slow. Symptoms were among the following.
  • slow scrolling
  • slow render times
  • bad video playback
  • slow tab switching
The problem is clearly related to the graphical rendering process. Worth mentioning is that on the same hardware the Chromium browser was snappy. After some trial, error and searching I found a single tweak that can be set to solve this issue! Iceweasel/Firefox utilizes XRender by default (see http://en.wikipedia.org/wiki/X_Rendering_Extension). XRender is a slow and often completely unaccelerated way of doing things. Configuring Iceweasel/Firefox to not utilize this extension will speed things up substantially. Recently a feature was added to the Mozilla branch to disable XRender (see https://bugzilla.mozilla.org/show_bug.cgi?id=743830). The setting for this is among the hidden configuration options. Open you browser and enter the following in the address field. about:config Acknowledge the warning message and promise me also that you will only change things here if you know what you a doing. At the top there is a search bar to search among the many many setting available. Go to the search bar and search for the following setting. gfx.xrender.enabled This is the setting that we want to change. Change this setting to False by double-clicking it in the list below. The line will turn bold to indicate that this setting is changed from the default value. Restart you browser and experience the snappiness. This tweak however may cause graphical glitches. There is a way to force hardware acceleartion and fix most of the glitches at the same time. If you do not experience any glithes you should not change this. layers.acceleration.force-enabled Setting this to True forces hardware acceleration (OpenGL) to be enabled. Keep in mind though that if you are using Xinerama you will only be able to use the web browser on the primary display. I actually ended up setting both of these tweaks with good result running Iceweasel 18.0.1 and NVIDIA 304.64.
by Sasha 2013-10-12 02:12 UTC
Brilliant, thank you for this simple and totally effective tweak! Was trying to find a way to get Iceweasel 20 to run like Firefox 24 after installing Crungbang linux, which happens to come with Iceweasel. Thanks!

by Sasha 2013-10-12 02:17 UTC
Sorry..., that should read "CrunchBang". Sorry to all those "CrunchBangers" out there!

by Daniel 2014-01-24 08:55 UTC
You are most welcome Sasha. I'm happy you found this information useful. I have found that these changes speed things up in most installations. Both settings are not always needed tough.

by Javad 2014-10-28 17:33 UTC
Worked like a charm :) My initial guess was that it is due to buggy NVIDIA driver.

by Mike 2014-12-12 22:12 UTC
This is the perfect solution ! I had always massive rendering glitches with Firefox making it completely unusable, but no problems with Chrome. Ubuntu 14.04 NVIDIA 304.125 Geforce Go7600

by inthief 2015-02-20 22:29 UTC
Excellent tweak. Thank You

by Kirk 2015-03-28 17:21 UTC
Turning off xrender dropped the hardware test from 16fps to 5; it's possible the hardware test depends on it (and I didn't try the force option) but now I have something to test with; thanks for pointing this out. https://developer.mozilla.org/media/uploads/demos/p/a/paulrouget/8bfba7f0b6c62d877a2b82dd5e10931e/hacksmozillaorg-achi_1334270447_demo_package/HWACCEL/

by klutt 2015-08-23 01:53 UTC
Exactly why should I avoid layers.acceleration.force-enabled unless I'm having rendering problems? Great tip btw.

by Daniel 2015-08-29 11:08 UTC
I'm not 100% sure but depending on your X configuration layers.acceleration.force-enabled may cause problems. Especially if you have multiple screens and not all of them support acceleration (different drivers, HW etc).

by Manuel 2016-05-13 22:07 UTC
Excellent, no more glitches and annoying rendering. Thanks

by seekhealth 2016-07-01 10:10 UTC
Very good post. It worked better when I applied the 2 recomendations.

by Cryss 2016-10-10 08:29 UTC
Wow! Both options work for me. Thanks a lot.

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