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I'd like to know when and how the firefox 4 plugins eats memory.

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Firefox RAM usage scales with available RAM in my use. On a computer with .5GB of ram I've seen it use 20k but on my 12GB device it can use over a GB with similar or same addons. It just runs way slower on the .5GB device. – Jeff F. May 18 '11 at 18:13
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At least with linux you can look for a process called plugin-containe. I assume its the same with windows.

Under linux you can use:

ps v -C plugin-containe

That will print out memory information about the process. That information refers to all plugins running in FF, because all run in the same process. I don't know if there is still any memory allocated in the main FF process related to plugins (e.g. some IPC overhead).

One of the printed information is a column with the percentage of your physical memory.

   %mem       %MEM    ratio of the process's resident set size  to the
                      physical memory on the machine, expressed as a
                      percentage. (alias pmem).
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In general, add-ons are not running as separate processes. Determining which are using a lot of memory should be simply a matter of turning the add-ons off one by one, then restarting the browser, noting memory usage of the firefox.exe process along the way.

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