The cycle collector heap dump is useful for figuring out why the cycle collector is keeping an object alive. These can either be manually or automatically generated.
To manually generate a CC dumpon Firefox 29 and up, go to about:memory and use the buttons under "Save GC & CC logs." "Save concise" will generate a smaller CC log, "Save verbose" will provide a more detailed CC log. To manuall generate a CC dump prior to Firfox 29 even in a non-debug build, enable the Error Console, by going to about:config and setting devtools.errorconsole.enabled to true. Then open a new window, go to Tools, Web Developer, Web Console.
Then evaluate this expression: