If you used to open lot of tabs in Firefox and work, inactive tabs always consume memory we’ve covered about:config tweak to speed up Firefox based on BarTab add-on which lets you load desired pages in background and all other tabs will be kept on BarTab, Dormancy is similar type of Firefox add-on checks for inactivity of tabs & automatically unloads them after 5 minutes they will be restored once when user selects or access them.
This may be an experimental add-on, aimed at users who don’t restore session, but useful for user having long running instances of Firefox and many tabs. Mozilla may land this as a core feature in Firefox 9. If the tab’s haven’t been selected for 5 minutes Dormancy considers those tabs as inactive, you can change below preference value in milli seconds.
Tab are checked for inactivity for every 5 minutes , to change this set below preference to a value in milliseconds.
Developer warns this add-on as experimental and recommends not to install if you use to restore session to load tabs and windows on startup.