Recently I started to observe this very confusing and annoying, not to say worrying behaviour when having Firefox open and then launching Chromium:

For around 30 seconds, Firefox' child processes would consume all available CPU resources, causing websites to stop render (already displayed page freezes, new pages show a white page with grey spinning circle) while the overall window is still responsive (menus, page scrolling, switching tabs, even internal pages like about:config or about:preferences work...). Chromium itself does not show any symptoms. Terminating Chromium again immediately, while Firefox is spinning, does not stop the behaviour any faster.

The same happens with my regular Firefox profile, a brand new, untouched Firefox profile without any add-ons etc., Firefox started in safe mode with add-ons disabled, and Firefox started in private mode. Similar for Chromium, I can launch it with my regular profile, in incognito mode or with a temporary profile, always generating the same results.

There is nothing odd happening when Chromium is running and I open Firefox.

When launching Firefox from a terminal, I sometimes get messages like these when I quit it while it is spinning (note the pipe error line mentioning some chromium ipc...):

ExceptionHandler::GenerateDump cloned child 32165
ExceptionHandler::SendContinueSignalToChild sent continue signal to child
ExceptionHandler::WaitForContinueSignal waiting for continue signal...
[Parent 26520, Gecko_IOThread] WARNING: pipe error (52): Connection reset by peer: file /build/firefox-8oo9jx/firefox-62.0+build2/ipc/chromium/src/chrome/common/ipc_channel_posix.cc, line 353
ExceptionHandler::GenerateDump cloned child 32274
ExceptionHandler::WaitForContinueSignal waiting for continue signal...
ExceptionHandler::SendContinueSignalToChild sent continue signal to child

Strangely I could not reproduce that behaviour in a guest account or a newly created regular (admin) account.

Some system specs (updated):

  • Ubuntu 16.04 (64 bit)
  • Firefox 62.0+build2-0ubuntu0.16.04.5 63.0+build2-0ubuntu0.16.04.2
  • Chromium 69.0.3497.81-0ubuntu0.16.04.1 70.0.3538.77-0ubuntu0.16.04.1
  • fontconfig 2.11.94-0ubuntu1.1
  • Graphics hardware: Intel SkyLake integrated graphics (i5-6200U) + Nvidia GeForce 940M
    Currently I have the nvidia-410 driver installed, but switched to the Intel prime profile. How can I further troubleshoot and fix this issue?

I made a performance profile with the Gecko Profiler Extension, installed to a clean fresh Firefox profile on my regular Ubuntu account. It can be found here: https://perfht.ml/2zpTWsh - The unresponsive time frame with 100% CPU usage should roughly correspond to the highlighted area on the Content Proc timelines, from roughly 18s - 56s.

I created a Mozilla bug report for this issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1504461

Important update: Apparently my bug report was a duplicate of https://bugzilla.mozilla.org/show_bug.cgi?id=1495900, which points out fontconfig as the culprit. Seems like starting Chromium is making a change in the font configuration somehow, which triggers a complete reload in Firefox. This fits the performance profiling report, and also aligns with how former updates to font packages have triggered the same kind of freeze.

Any ideas how I can make the three (Firefox, Chromium, fontconfig) behave nicely along each other?

  • All I'm finding at line 353 of ipc_channel_posix.cc is a return true statement. Of course Connection rest by peer being fatal never bodes well. Sadly I cannot reproduce this problem. I wish I could be of more help. – Elder Geek Nov 2 '18 at 14:45
  • I also had sporadic issues w/ high cpu on ubuntu, but I can't say what caused it, or resolved it. There were numerous open issues that I was tracking related to high cpu usage--so, I'd upgrade, and hope. Currently, I'm not having any issues (or if I do, it's a specific tab; so, restarting the browser or closing the tab resolves it). Is it possible to upgrade from 16.04 to 18.10 (as, of course, 16.04 is from 4/2016 and 18.10 is as of 8/2018)...? And, fwiw, I've also switched to kubuntu which seems to gives me fewer headaches. (If possible, boot from USB & experiment w/ both.) – michael Nov 3 '18 at 6:57
  • Sometimes I have Firefox running and then open Chrome (I know it's a little different) and haven't noticed any high CPU usage. Perhaps 5 second spike from 18% CPU to 30% CPU across 8 virtual CPUs. – WinEunuuchs2Unix Nov 3 '18 at 23:31

TL;DR: It's an issue with fontconfig before version 2.13. It can be fixed by upgrading the package to 2.13 or higher (though I couldn't find a suitable provider). Alternatively, examine all your fonts-related folders and config files in your home directory and test if removing any of them resolves your issue. For me, renaming ~/.fonts did the trick.

After learning about the bug reports https://bugzilla.mozilla.org/show_bug.cgi?id=1495900 and https://bugzilla.mozilla.org/show_bug.cgi?id=1411338 it becomes rather clear that the problem must be caused by fontconfig.

Somehow when Chromium starts, it triggers a change in the fonts database (???), which causes Firefox - if currently running - to re-scan the file system for fonts somehow, resulting in the CPU usage and temporary freeze.

Apparently updating the fontconfig package from version 2.11 to 2.13 (the version shipped e.g. in Ubuntu 18.10) should fix the issue, but I found no easy way to get that version on 16.04, without breaking dependencies of lots of other packages I have installed.

So as the issue is limited to my user account, I examined my user's local font configuration and folders. There's quite a mess of different font-related directories to be honest, including ~/.fonts, ~/.local/share/fonts, ~/.local/share-font-manager, ~/.config/font-manager, ~/.cache/font-manager, ~/.cache/fontconfig and a few more config files and application-specific font stuff.

I started by removing (renaming) the ~/.fonts folder, as it didn't seem to contain anything useful anyway, and a simple touch ~/.fonts/Library/ before that triggered the Firefox misbehaviour. After that folder was gone, so was the issue when launching Chromium. \o/

  • Makes sense as I have no ~/.fonts directory. All fonts are in a system wide directory. – WinEunuuchs2Unix Nov 4 '18 at 1:02
  • Apparently a similar or even the same bug can be triggered on 18.04 by launching a root terminal window too. strace indicates some serious file i/o regarding font files. Interestingly this is not only a problem with firefox alone but other xorg applications as well so i presume a problem within xorg as well. Unfortunately deleting the directories in question did not help. – stefanct Dec 7 '18 at 23:48
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    However, upgrading fontconfig to 2.13.0-5ubuntu3 from cosmic/18.10 did solve the problem AFAICT. This was the weirdest bug in a while... thanks for the pointers. – stefanct Dec 8 '18 at 0:23
  • @stefanct how did you get it to install without breaking stuff, i tried forcing fontconfig and libfontconfig1 2.13 and apt wanted to remove my entire DE, running 18.04 – GM-Script-Writer-62850 Dec 13 '18 at 1:57
  • @GM-Script-Writer-62850 I have not any remembrance of dealing with libfontconfig1 specifically. In general I have added the bionic mirrors to apt's list and apply apt pinning to avoid installing any of its packages w/o telling it specifically. Then I simply used apt's -t option like so: apt install fontconfig -tcosmic. I am using mate as DE… maybe it does not work as easily with other DEs. – stefanct Dec 13 '18 at 4:05

Don't know if the following suggestion will work or not. You can give a try. Try removing chromium and firefox completely (keep the .deb files of course) using Synaptic Package Manager. After that check if there are any broken dependencies. Fix them using synaptic (if any). Now check for the CPU usage (I use Powertop).Finally do a fresh re install of the browsers.

Note: These things are generally what I do in case of specific abnormalities. I remember facing a slightly similar issue a year ago. It got resolved this way.

  • Nope, purging and reinstalling all firefox* and chromium* packages did not change anything. – Byte Commander Nov 3 '18 at 17:23
  • does the idle stats and frequency stats widgets of powertop show 100% usage when you launch chromium ? – Hirak Nov 3 '18 at 17:40
  • Yes, it shows around 112% for "C0 active" on every core in idle stats, and frequency stats report the maximum frequency (2.7GHz) and 0% idle on each core. The overview tab displays all the Firefox processes on top of the list, with roughly 600-900ms/s computing time each, but zero events/s. – Byte Commander Nov 3 '18 at 17:48


It has been proposed this Firefox Bug 1492360: High CPU usage when open firefox before chrome/chromium. That is is a duplicate of Bug 1495900: Starting Chrome makes Firefox content processes hang for about two minutes, due to FontConfig font rescanning (FcInitReinitialize), is the culprit.

But I'm on Firefox too:

Firefox version.png

And when I open up Chrome:

Chrome version.png

I don't see any performance hit to CPUs.

It may be against your morals but perhaps you can try installing google-chrome-stable like I have. Then do the test again. If there is no CPU usage spike to 100% then a bug report could be filed between Chromium and Chrome.

I'm on Ubuntu 16.04.5 LTS. Although kernel is currently 4.14.78 LTS chain I don't think that has anything to do with it as I didn't notice CPU hits on previous kernels either.

The only time I see all CPU's at 100% is during update-initramfs.

fontconfig verson

In the bug report it is revealed:

$ dpkg -l 'fontconfig*' | grep "^ii"
ii  fontconfig        2.12.6-0ubuntu2 amd64        generic font configuration library - support binaries
ii  fontconfig-config 2.12.6-0ubuntu2 all          generic font configuration library - configuration

In my non-buggy version (could be because of no local fonts though):

$ dpkg -l 'fontconfig*' | grep "^ii"
ii  fontconfig        2.11.94-0ubuntu1.1 amd64        generic font configuration library - support binaries
ii  fontconfig-config 2.11.94-0ubuntu1.1 all          generic font configuration library - configuration

I'm at 2.11.94 version earlier than bug report 2.12 version. In bug report upgrading to 2.13 is a recommended solution but OP mentioned in comments this isn't possible. As such 2.11.94 might be an option.

  • Well no, I don't intend to install Chrome. However, I found out that the culprit is fontconfig now. Probably you have different (or no) local fonts installed in your user account. I found a workaround of removing (renaming) the ~/.fonts folder, which fixes the issue. Apparently also upgrading to fontconfig >= version 2.13 should fix it, but I can't do that on 16.04. – Byte Commander Nov 4 '18 at 0:30
  • Yes the only fonts I've installed are for bar codes (code 3 of 9) which are ttf and used in word processors / spreadsheets. Unfortunate you had to solve your own bounty question but if it's any consolation the same has happened to me in the past. – WinEunuuchs2Unix Nov 4 '18 at 0:37
  • I added downgrading fontconfig as an option to match my version but that is a "faint hope" given you may have come from there. If you have a link for installing local fonts I'll give that a try to confirm/deny the effect of older fontconfig version. – WinEunuuchs2Unix Nov 4 '18 at 0:47
  • My version of fontconfig is 2.11.94-0ubuntu1.1 too, that one is not bug-free. It must be a combination of the installed fonts, custom font configuration and black magic, I guess. Check my answer. :) – Byte Commander Nov 4 '18 at 0:50

Bumblebee's performance has been known to be relatively buggy. nvidia-prime has been known to drain laptop batteries. Check these two, which one works or is better for your system, either Nvidia with Bumblebee or nvidia-prime. Check which works better, with Nvidia discrete graphics enabled or disabled.

  • Sorry, but your answer does not help. Preload is installed for years already, and I also increased the cache capacity as you advised. The smart size value does not exist for me though. Anyway, there was no change in the described behaviour. I still have Firefox running on 100% CPU and its content tabs becoming unresponsive for half a minute whenever I open any new Chromium window. To be honest I don't even see why caching would actually effect this at all... – Byte Commander Oct 28 '18 at 15:40
  • @ByteCommander I start having the same issues, using Ubuntu 16.04 and 18.04. I change my swappiness and my cache but nothing worked, in the end my solution, and I am very happy with its behavior, was installing Lubuntu 18.04. May be is something you should ponder about... – ft18 Nov 2 '18 at 3:41
  • I just noticed you edited your answer @karel. So I've purged nvidia drivers and bumblebee and tried to wipe all residual traces, then checked out if the issue persists with just nouveau drivers, installed nvidia-410 (previously using 369) and tried with both the nvidia and intel prime profiles. My issue of Firefox freezing and spinning 100% CPU whenever a Chromium window opens stayed the same. :( Any remaining ideas? – Byte Commander Nov 2 '18 at 20:49
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    I don't consider switching to Lubuntu an alternative. I like Unity and my hardware is well above the requirements for any flavour. My 12 GB of RAM are not the issue. – Byte Commander Nov 2 '18 at 20:51
  • I started Firefox with a clean, fresh profile (no add-ons, settings, history etc) and I started Chromium with a temporary profile, still the same issue. – Byte Commander Nov 3 '18 at 13:18

Judging from the log, it looks like Firefox is using synchronous IPC (Inter-process communication) for some reason. There are flags in Firefox to turn on synchronous IPC explicitly (eg: network.cookie.ipc.sync). One of those might be enabled. You can access these from the about:config page

The delay would then be a result of firefox waiting on the response. Since there is no load when Chromium has finished starting up or is not actively running, there is an immediate response.

Related: https://bugzilla.mozilla.org/show_bug.cgi?id=1331680

  • I toggled the value of this network.cookie.ipc.sync config from false to true and back, restarting Firefox after each change, but still the same behaviour :( I still don't get why Firefox and Chromium would even communicate in the first place, they should mind their own business each. – Byte Commander Nov 3 '18 at 12:34
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    I had deleted this since you found the actual reason to be unrelated, but I guess I should leave this here as probable cause? – Aswin B Nov 4 '18 at 19:36

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