From MozillaZine Knowledge Base
Rather than wait until a page has completely downloaded to display it to the user, Mozilla applications will periodically render what has been received to that point. This preference controls the maximum amount of time the application will be unresponsive while rendering pages.
Possible values and their effects
The maximum number of microseconds (1 second = 1,000,000 microseconds) between reflows. (Default: triple the value of content.notify.interval)
First checked in
Has an effect in