A New Cache back-end for Firefox was landed on Nightly channel and is not enabled by default. According to Mozilla developer Honza Bambas blog post, role of New HTTP Cache in Firefox is to keep the cache content after crash or a kill and doesn’t cause any UI hangs. This new cache is hidden behind a preference in about:config. Mozilla planning to enable new HTTP Cache by default for Q4/2013 in Firefox.

How to Enable new HTTP Cache in Nightly?

1. Visit about:config in browser.

2. Find the preference browser.cache.use_new_backendand, double click on it and give integer value as “1”,  you don’t need to restart the browser for the changes to take effect.

When this Preference value set to 1, Firefox uses new HTTP Cache and when set to 0 browser uses old cache. You can switch been Firefox old and new cache by toggling the preference value.

Honza says “there are still open bugs before we can turn this fully on.  The one significant is that we don’t automatically delete cache files when browser.cache.disk.capacity is overreached, so your disk can get flooded by heavy browsing.  But you still can delete the cache manually using Clear Recent History.”

Source: @Firefoxnightly