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Firefox on Vista has been grinding to a crawl and I just checked the RAM usage on this machine and found 400MB of RAM in use by Firefox.

Is this because of plugins/addons?

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400 MB? that all?? consider yourself lucky! :) – Molly7244 Dec 5 '09 at 19:50
How many tabs/uptime? That really isn't that bad. Chrome takes an average of 125MB for every tab process here, 250MB each for GMail and FB – prestomation Dec 5 '09 at 20:01
I see these questions all the time, and I don't understand how the numbers can get so high for people. They must have like 30+ add-ons installed or something, because I haven't had Firefox break 250MB since version 3.0 came out. – Sasha Chedygov Dec 5 '09 at 20:14
you see these question all the time because the memory leaks of the Gecko engine are known issues since day 1 and after all these years they haven't yet managed to address the problem in a satisfactory way. as for the screenshot i have posted above, Flashblock and NoScript are the only two addons installed and maybe a dozen tabs open at the time. and yes, the insane figure is related to the uptime. but then, i have no use for browser that i have close every few hours in order to purge the memory. – Molly7244 Dec 5 '09 at 20:52
Right, I know about that, but I don't understand how the figures can be so high for some people and so low (relatively speaking) for me and others. I guess it depends on the pages you visit, but it still seems weird. – Sasha Chedygov Dec 6 '09 at 0:43
up vote 2 down vote accepted

Not answering your actual question ("why?"), but suggesting a solution to high memory, the AFOM addon:

recovers Memory Leakage within a running instance of the Firefox browser application.

Works really well, reduced my average usage from 250MB to 80MB.

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PLugins do play a major factor, yes. It could also relate to the number of tabs you have open, or the amount of Flash or JavaScript that is running on a page you have open.

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Have you tried running Firefox in "safe" mode with no plugins and addons enabled?

Check the memory then and see if it makes a difference. If it does then your answer is "yes".

Also check memory with 1 tab open against your usual number. If you have lots of tabs open then you're going to have lots of pages in memory. It all adds up.

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Here's a list of "problematic" plugins/extensions; maybe it is one of them.

This doesn't answer "why" but I thought it was an interesting comparison of how much memory the browser uses:

Have any of you tried the memory managing/saving plugins for firefox? Helps save memory from unused tabs: TooManyTabs Firefox Addon

I think there's a few more...

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Plugins + # of Tabs + Content of Tabs

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