How to Determine which Firefox Add-ons are Using the Most Memory

"I usually deal with Firefox memory issues by installing two different Firefox'es on my computer.
The first one is the default Firefox and the other is portable Firefox.

I install all the addons I am ever going to use on the portable Firefox (FF)
I install the addons which are used almost daily on the default Firefox.

This way I can use the addon just by switching over to the portable Firefox.

If this is not the solution you are looking for then try these addons

AFOM - AFOM recovers Memory Leakage within the Firefox application. (Windows only)
NOTE: This add-on has been removed by its author.
CacheViewer - Allows searching and sorting memory and disk cache files.
CacheViewer is discontinued please use CacheViewer Continued.
EDIT: I tried it, and it shows all the files used by Firefox in the cache which eat up precious memory.
bosskey - Add Boss Key, Minimize/Close to tray and memory auto cleaning to Firefox.
RAMBack - RAMBack will cause Firefox to issue an internal notification to free up memory that is otherwise held for performance purposes."

"Only slightly less tedious:

Check memory usage of Firefox + all plugins.
Disable them all & check memory usage - difference is due to plugins.
Enable half a dozen (say), check memory usage.
If the increase is not too great repeat with the next batch.
If the increase is a large proportion of the usage then disable that batch and check each one individually.
Repeat until all plugins added.

Obviously this is probably a non starter if you have lots of plugins.

Searching for more information on those plugins might tell you something as well."