It appears that the browser toolbox is retaining any source string that is visited until it closes. I can find lots _longStringActors that are retaining JSStrings. Steps to reproduce: * Open up browser toolbox. * Take a memory snapshot in the browser toolbox * Navigate in the browser to a source-heavy site, e.g. cnn.com * Navigate to about:blank * Take a memory snapshot in the browser toolbox. * Switch over to dominator tree and observe the large amounts of retained strings. * (See the attached screenshot) Expected Results: * I would expect that as you navigate away from sites, those strings would be garbage collected. Actual Results: * Strings are retained forever, even when navigating between pages, and closing tabs.

Given the appearance of "netEvent", I am going to guess this is from the network monitor. Adding up all of the following: * The network monitor holds onto all request and response bodies (bug 1297525) * The network monitor is started eagerly (on toolbox open of any tool) * The browser toolbox is monitoring every page this means the Browser Toolbox will hold many, many strings for every tab, as you noticed. Perhaps for only the Browser Toolbox case, we should make the network monitor be lazy again. (I am assuming eagerly starting is still considered useful for a single tab...) :Honza, any thoughts?

Ah, nice find jryans!