I had this problem and found that it was caused by a specific Flash advertisement on a page that I visited often. The flash file used a random falling snowflakes effect which used huge amounts of CPU, especially on single-CPU machines.

I have had a similar problem where unknown content on certain web pages cause plugin-container.exe to use high CPU usage. My Pentium (4) 2.80 GHz CPU starts roasting, using 100% for plugin-container.exe. The offending content may have been specific advertisements. I can go to the same web page another time and I don't have the problem.

On older versions of Firefox without plugin-container.exe, that same situation would cause Firefox to use high CPU usage. As soon as I back off the page the high CPU usage would subside, as it still does now.

I don't have many plugins and I suspected the Flashplayer, so I first disabled plugin Shockwave Flash (10.0.22.87) and the problem immediately stopped. I enabled the Shockwave Flash plugin, and again had the problem. So for me, the problem was pinpointed.

I looked for a newer version of Shockwave Flash for Windows XP 32-bit (Firefox) and so far have not had any success.

I tried the "Check to see if your plugins are up to date" link from the Add-ons Manager. That takes me to the Mozilla Plugins check page, but the page status gets stuck at "transferring" even though Bytes are no longer being received and nothing ever shows for the status of my plugins. I had several plugins enabled at the time, including Shockwave Flash. That Mozilla Plugins check page has never worked for me.

EDIT I found the latest version of Flashplayer (11.1.102.55) on the Adobe site and downloaded the installer file. I ran the installer and the download status window appears and after a short while, I get the message, " Can not find reliable source." I tried again, and the second time I get the message, "Download timed out." I guess the Adobe servers are down.

I tried running the installer application one more time and now I get script errors when I run the installer, before the download initializes. I have to close the installer with Windows task manager.

EDIT I finally downloaded the full file version of Adobe Shockwave Flash version 11.1.102.55 and installed it. It was impossible to use the Adobe installer application download, since it doesn't get a reliable connection to a server when it is run.

Anyway, with the latest Shockwave Flash version I still get hi CPU usage for plugin-container.exe on certain web pages with advertisements.

OK, I have followed all steps listed in the following article.

"The plugin-container.exe is using 100% cpu usage???"

With only Shockwave flash 11.2.202.235 runninng, which has to be for video to play, I am still having the problem.

I upgraded from XP to Windows 7, and installed a new video card.

I also tried the Beta version of FF.

The plug-in is still using 50% of my CPU.

Problem doesn't occur in IE9.

But hey, if I wanted to use IE I wouldn't be making this post.

I have also installed the following add-ons- Adblock pluss 2.03 Flashblock 1.5.15.1 and enable my "Symantec Intrusion Prevention 10.1.1.8".

After enabling these add ons there was and increase in FireFox CPU ussage. This seems to spike off and on depending on my surfing activities.

I suppose I can live with this.

Notice from moderator
This thread is being locked due to its large size which is making it hard & confusing to give support to specific individual users. So to avoid a unorganized situation like this, it helps us give you one-on-one support if you post in a thread of your own.

To start a new thread, use this link: https://support.mozilla.org/en-US/questions/new

The main reason we ask people to do that, is that a new thread will auto detect info about your system like your OS, Firefox version and Plugins. That way we can look and see if anything stands out. Also make sure you fill out the Troubleshooting Information section by going to Help > Troubleshooting Information in Firefox and copying and pasting that info there using the "Copy to clipboard" button. It'll help us see what add-ons (which are different from plugins) you have and if we see you have one we know is a troublemaker we can tell you really quick.