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Firefox is unbearably slow after updating to version 27

  • 81 réponses
  • 606 ont ce problème
  • 20 vues
  • Dernière réponse par petef

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After updating to Firefox 27 all webpages take a few dozen seconds to several minutes to load. When loading a webpage Firefox's status displays "connecting" and the CPU gets maxed out with 95 to 100% of its cycles taking by Firefox.

The computer is older so it is a little slow but Internet Explorer 8 has no trouble opening the webpages and neither do other computers on the LAN so it is not a network issue. I have tried restarting Firefox, disabling add-ons, deleting add-ons, disabling hardware acceleration, restarting the computer, and reinstalling Firefox after wiping every trace of it and its user data from the hard drive and registry.

CPU: AMD Athlon 2800+ 2.08GHz RAM: 1GB OS: Windows XP Home Edition Service Pack 3 32bit

Comments by a forum moderator.
(Modified April 30, 2014 12:11:58 PM BST by John99 ) ~J99
Rather a long thread so I will add some comments here where easily seen.

 Modified June 18, 2014 6:08:41 AM PDT by John99

Modifié le par John99

Toutes les réponses (20)

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Were you using Firefox 26 just before Firefox 27?

When you mention disabling Add-ons, do you mean that you tested in Firefox's Safe Mode? If not, it's a standard diagnostic tool that disables extensions as well as JavaScript compilers and various customizations. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the dialog, click "Start in Safe Mode" (not Reset)

Any difference?

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jscher2000 thanks for the quick reply. Safe Mode makes no difference.

Modifié le par hj21c1yg

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Are there any firewalls, content filters / parental control filters, web reputation checkers, or proxies (whether local security software proxies or private VPN or TOR) that stand between Firefox and those websites which might be slowing things down?

  • You can check your proxy settings using:

    orange Firefox button (or Tools menu) > Options > Advanced > Network mini-tab > "Settings" button

    The default setting is "Use system proxy setting" but you also can try "No proxy" to see whether that makes any difference.
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It is possible that your security software (firewall, anti-virus) blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.


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@jscher2000 There are no software based content filters / parental control filters, web reputation checkers, or proxies. Hardware wise there is only the router be between Firefox and the internet. The only firewall is the default Windows XP one which to my knowledge only blocks inbound connections unless it has been tweaked and it hasn't.

The proxy settings were set to the default setting of "Use system proxy setting". Switching to "No proxy" results in a fast/normal load of some webpages but on others there is no difference which is kind of weird.

@cor-el Thank you also for your speedy response. As mention above the firewall should not be an issue. I had a very light weight anti-virus installed but I failed to state above that I uninstalled it when trying to find out what was wrong so that also should not be an issue.

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Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

If the new profile works then you can transfer some files from an existing profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem.

Do a malware check with some malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.
All these programs have free versions.

Make sure that you update each program to get the latest version of their databases before doing a scan.

You can also do a check for a rootkit infection with TDSSKiller.

See also:

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@cor-el As regards to creating a new profile perhaps I was not clear enough in my first post one of the things I have already done is uninstall Firefox and delete the user data after backing it up.

I then used forensic software removed any remaining traces of Firefox or data generated by it from the system (i.e. remnants like files/folders to the installation, profile or registry keys etc... that the uninstaller missed).

After which I reinstalled Firefox if that is not a new profile overkill I don't know what is.

In reference to malware I am very certain that is not the issue.

The computer runs on a limited account and is regularly and aggressively scanned both by the installed anti-virus program and by live CDs.

In addition I majored in computer science and have a background in computer security, if the system was infected I kind of think I would know it.

Modifié le par hj21c1yg

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Could you open Firefox's Web Console (Ctrl+Shift+k) and click the Network button on the black toolbar, then navigate to a page and look at the timings for where you see delays.

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Same problem here under Windows XP – appears to be related to Adobe Flash Player (I upgraded to the latest release,, when I upgraded to Firefox 27). Any page with Flash content kicks off the problem; successive similar pages increase the problem until the Firefox process becomes CPU bound. Temporary workaround (other than restarting Firefox) is to select Tools>Add-ons>Plugins, and then change the activation setting for Flash from "Always Activate" to "Ask to Activate".

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Ditto. After upgrading to V27 on 2 different PCs all sites, but especially secure sites (including Amazon, Wells Fargo, UPS, USPS, and Southwest Airlines), were so slow as to be useless. Tried everything: disabling plugins, doing a reset, offering chocolate to the browser gods, and all the other recommended tricks. No joy.

Finally, in desperation I downgraded back to V26 and everything is now fine and all sites are running at normal speeds. I turned of the auto-update feature until this gets fixed.

I think someone stepped in the brown stuff with V27.

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Hmm, my "Ask to Activate" Flash workaround, that seemed to help on my home PC, does not appear to have the same beneficial effect on my work PC (also Windows XP SP3, Firefox 27, Flash I think I too will downgrade to Firefox 26 for now.

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Interesting but my flash player claims to be version 11.9.900.117. Don't deliberately use it much so I haven't upgraded it in a while. The mystery deepens. I'd think the Mozilla folks would get on finding a real solution to this problem ASAP.

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Like FrogAZ, I downgraded to V26 and everything is back to normal – that is, Firefox loads all sites in a timely fashion. (The Firefox process no longer becomes CPU bound, even with Flash always activated, suggesting Flash alone is not the problem.) I too have turned off the auto-update feature until the problem with V27 is fixed.

Note I downgraded using the method described by phorensik in the support article How do I downgrade?. Look for the part headed "DOWNGRADiNG WITHOUT NEW INSTALLING AND KEEP ALL SETTINGS". The method worked beautifully for me.

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Firefox 26 and now 27 running in Ubuntu 12.04 have been very slow to open new pages - sometimes as long as 2 minutes. Chromium, on the other hand opened the same pages in less than 3 seconds. Using Wire Shark to analyze network traffic, we found that Firefox was querying the WINS name server a very large number of times number of times causing 300 ms delays in each query. (For some sites like the New York Times, there were more than 100 WINS queries.

In the network configuration files, we found that WINS was listed before DNS in the list of name servers to query for looking up domain names. By editing /etc/nsswitch.conf to place WINS at the end of the name server list we were able to make Firefox open pages as fast as Chromium.

To make this change, in a terminal type

sudo gedit /etc/nsswitch.conf

enter the password and change the line that reads

hosts: files mdns4_minimal [NOTFOUND=return] wins dns mdns4

to read as follows:

hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4 wins

Save the file and exit. Then reboot your computer. This will make WINS the last name server query for name lookup.

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I had a very similar issue on a similar computer (Windows XP SP3, Pentium 4 2.4GHz, Nvidia GeForce FX 5500), and it came down that in my case the slowdown was simply introduced by animations (I believe the simple rotating icon on the tab was enough to slow the loading of a webpage).

The CPU used to reach around 100% in Kernel mode (for info this is the red line in the Windows Task Manager. To enable it go to the "Performances" tab then in the "View" menu ensure "Show kernel times" is selected).

To know if you face the same issue:

  • Type "about:support" in the address bar and press Enter.
  • In the "graphics" section check the line with the entry "AzureContentBackend".
  • If the value is "cairo" you may well face the same issue than I did.

In that case I have found a workaround:

  • Type "about:config" in the address bar and press Enter.
  • Search for "".
  • The value should be "direct2d,cairo". Edit it to be simply "direct2d" (ie. remove "cairo"), then restart Firefox.

I have already filled a bug report which can be found here:

Feel free to add feedback if you have the same issue.

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" Type "about:support" in the address bar and press Enter.

   In the "graphics" section check the line with the entry "AzureContentBackend".
   If the value is "cairo" you may well face the same issue than I did. 

In that case I have found a workaround:

   Type "about:config" in the address bar and press Enter.
   Search for "".
   The value should be "direct2d,cairo". Edit it to be simply "direct2d" (ie. remove "cairo"), then restart Firefox. 

I have already filled a bug report which can be found here:"

This solution worked like a champ on two different XP SP3 boxes. Thank you!

Modifié le par waveulator

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@jigebren - Perfect. Your solution about changing the value by removing "cairo" worked perfectly, in less than 30 seconds! OS=W7. THANK YOU X 1000!

Modifié le par pashadad

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Mine already says "direct2d" but its still lagging terribly.

EVERY web site takes forever to load. I have a Sony vaio laptop. Windows 7 Only 3 years old. In great shape.

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@Halofromsue - Are you actually in the case were it worked with v26 and the slowdown was introduced by the v27 update?

And you should try to delete "direct2d" as well in "" before restarting Fx (in my case I had no reason to delete "direct2d" because I knew it won't be used on my computer anyhow).

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Hi Halofromsue, if you want to try reinstalling Firefox 26 (do not remove Firefox 27 first) you can get a link in this article: Install an older version of Firefox. Please report back on whether that makes any difference in your case.

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