Why does firefox cause two-second LAN latency every five seconds?
Under Windows 8.1 at least, if I use Firefox for a while, I get negative bandwidth spikes and high latency every five seconds. According to the windows task manager, firefox is not using a large amount of bandwidth. If I'm downloading something, even in a program other than Firefox, the network usage drops to zero for a second every five seconds. This is not due to an add-on, because a blank profile comes to the same result.
I would attach a screenshot of a ping to the local router and a network usage graph, but the image will not upload.
Krejt Përgjigjet (4)
Here is the screenshot I couldn't upload before.
If it happens in Firefox and other programs, it's in the computer or modem.
Have your ISP test your service.
Unplug the power to the modem for a slow 10 count to re-boot it.
You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.
Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.
It only occurs when Firefox is open. Sometimes not immediately after I start Firefox, but the problem goes away as soon as I close Firefox. It's not a matter of Firefox merely being a program that uses the network. Chrome does not cause this, nor does Steam when it's downloading a game.
Have you tried Safe Mode in Firefox (I know you said you tried a new profile)? How to start Safe Mode: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode#w_how-to-start-firefox-in-safe-mode.
Safe Mode is making extra sure.
PS. I would run the malware scans as suggested by Fred; this sort of behaviour is suspicious. You should also check what connections are made from and by Firefox. Speccy, http://www.piriform.com/speccy, can show you connections on its Network tab.
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