During development of XUL applications, it’s convenient to disable the XUL cache so that changes you make to files on disk take effect the next time the window or dialog is loaded (instead of the next time Mozilla starts).
Possible values and their effects
True: Do not cache parsed XUL documents and do not save the cache to the XUL FastLoad file on exit; re-read the source files each time the window or dialog needs to be displayed.
False: Cache XUL documents in memory and save the cache to disk on exit to improve performance. (Default)