Browser.cache.check doc frequency
From MozillaZine Knowledge Base
When a page is loaded, it is cached so it doesn't need to be downloaded to be redisplayed. If the page changes after a previous visit, you may want to redownload it anyway to get the updated page. This preference controls how often to check for a newer version of a cached page.
Possible values and their effects
Check for a new version of a page once per session (a session starts when the first application window opens and ends when the last application window closes).
Check for a new version every time a page is loaded.
Never check for a new version - always load the page from cache.
Check for a new version when the page is out of date. (Default)
Edit -> Preferences -> Advanced -> Cache -> Compare the page in the cache to the page on the network:
First checked in
Present since at least 1998-03-27.
Has an effect in