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Firefox is unbearably slow after updating to version 27

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New User

Firefox is unbearably slow after updating to version 27

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

81 REPLIES
Mozilla Support Contributor

Re: Firefox is unbearably slow after updating to version 27

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: Troubleshoot Firefox issues using Safe 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?

New User

Re: Firefox is unbearably slow after updating to version 27

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

Mozilla Support Contributor

Re: Firefox is unbearably slow after updating to version 27

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.
Site Moderator

Re: Firefox is unbearably slow after updating to version 27

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.

See:

New User

Re: Firefox is unbearably slow after updating to version 27

@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.

Site Moderator

Re: Firefox is unbearably slow after updating to version 27

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:

New User

Re: Firefox is unbearably slow after updating to version 27

@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.

Mozilla Support Contributor

Re: Firefox is unbearably slow after updating to version 27

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.

2014-02-09-21-24-21-e995ae.png
New User

Re: Firefox is unbearably slow after updating to version 27

Same problem here under Windows XP – appears to be related to Adobe Flash Player (I upgraded to the latest release, 12.0.0.44, 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".