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Many extensions lie inactive when I'm not using them like Firebug and Xmarks. Do they add to the memory footprint while they're sleeping. I'm not talking about disabled extensions.

Coz, if they are consuming memory, I'm better off disabling some of them which I don't plan to use often.

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up vote 2 down vote accepted

This will depend on each extension and how it was built. Some extension may consume memory even while not being used because they may load objects into memory as part of their startup code. Extensions with static objects or objects with static data members will consume memory too.

You have one great way to test which extension may be more problematic in terms of memory consumption while not being used.

  • Disable all your extensions. Open Firefox and note its memory consumption under task manager on Windows. Enable one extension at a time and restart firefox. Note changes in memory.

One last thing to take in consideration. Even if an extension does not consume (much, or any) memory while not being used, it may do so after it has been used. Firefox likes to cache objects for later use once these have entered the memory space. An extension may not be in use, but since it has just a few minutes ago, it's memory footprint (or part of it) may remain cached for the whole firefox session. As long as the cache isn't exhausted by other objects, it will stay there.

One last thought that occurred to me:

An extension is installed by default only to the current Firefox Profile. You can manage your extensions on different profiles with tools like Mr. Tech Toolkit, enabling and disabling extensions on a profile basis. As such, if you are concerned with memory, an alternative to manually disable and enable extensions is to create a few Firefox profiles. One with no extensions, another with all extensions and as many as you like with some but not all extensions. I'm imagining something like the following Profiles:

  • Clean (no extensions)
  • Developer (developer specific extensions)
  • Social (social web & blog extensions)
  • Full (all extensions)
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dats informative! I just did this experiment and here are the results backing ur answer: with StumbleUpon, Firebug & Xmarks enabled consumption is 33724K with all three disabled consumption is 24224K Around 28.17% less consumption with extensions disabled! I tested three times, results are more or less same – detj Oct 29 '09 at 1:20

Yes, they are most likely consuming memory because they are adding to the memory that firefox uses. However, since you aren't using them, the difference is negligible. For best memory performance, disable any addons that you don't use frequently.

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In my (limited, not rigorously trialed) experiments, an extension that is disabled won't use any firefix memory resources.

However, I'm currently trying to work out what is making scrolling in gmail so slow. I believe that a theme that is disabled but still installed is having an effect.

In concusion: I don't know. They shouldn't, but some maybe do. Sorry that it's not conclusive. I'd love to read some knowledge based answers! +1 for the question.

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