Hello Kate.

It's possible that you are having a problem with some Firefox add-on that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons (just to check), to see if Firefox goes back to normal?

Whenever you have a problem with Firefox, whatever it is, you should make sure it's not caused by one (or more than one) of your installed add-ons, be it an extension, a theme or a plugin. To do that easily and cleanly, run Firefox in safe mode (don't forget to select Disable all add-ons when you start safe mode). If the problem disappears, you know it's from an add-on. Disable them all in normal mode, and enable them one at a time until you find the source of the problem. See this article for information about troubleshooting extensions and theme and this one for plugins.

If you need support for one of your add-ons, you'll have to contact its author.

Firefox 3.6.4 and 3.6.6 use a process called, "plugin-container.exe" which was using up most of my CPU when I opened up multiple tabs that contained Adobe Flash files, and caused Firefox to lock up.

My solution was to use Firefox 3.5.10 which you can get from the Mozilla website at http://www.mozilla.com/en-US/firefox/all-older.html I am using Adobe Flash 10.1.53.64 without any problem in this version of Firefox. Check the release notes, I believe it contains all the latest security fixes in "Firefox 3.6.4".

Hopefully, they will fix Firefox 3.6 in the next version (e.g. Firefox 3.6.7), until then you should probably use "Firefox 3.5.10".

Michael, all future versions of Firefox will use plugin isolation (i.e. the plugin-container). According to what you say, you seem to be having a problem with Adobe Flash plugin, rather than Firefox itself. You should contact Adobe to report them your problem.

Morbus, I'm not saying Firefox should or should not have plugin isolation (it sounds like a good idea, if it works).

But, I will say Adobe Flash works fine in Internet Explorer and earlier versions of Firefox without plugin isolation (e.g. Firefox 3.6.3, 3.5.10). It only seems to have a problem with Firefox 3.6.4 and 3.6.6 which uses the "plugin-container.exe" process. So, given that Flash works in other browsers, maybe its "plugin-container.exe" that has the problem.

The user above may have problems, if the pages being loaded contain Flash files, or other files processed by "plugin-container.exe".

You can investigate further if you want, but I'm happy using Firefox 3.5.10 for now. Bye.

"But, I will say Adobe Flash works fine in Internet Explorer" Adobe Flash for Internet Explorer is not the same as Adobe Flash for Firefox. Please make sure your Adobe Flash is up to date, using this page, and then make sure your Adobe Flash for Internet Explorer is up to date, using the same page (it works for different browsers too).

"So, given that Flash works in other browsers, maybe its "plugin-container.exe" that has the problem. " Maybe, but I'm not aware that any bug has been detected with Firefox's plugin container. I'm not a developer, mind you, but you can check bugzilla and see for yourself. Besides, it's the plugin's job to be compatible with the browser. Plugins are made for the browser, not the other way around. This shouldn't be a simple matter of incompatibility, though (unless you're using an outdated version of Flash, of course), since the vast majority of users have no problem whatsoever.