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. Because reflowing the page every time additional data is received greatly slows down total page load time, a timer was added so that the page would not reflow too often. This preference specfies the minimum amount of time to wait between reflows.
Possible values and their effects
The minimum number of microseconds (1 second = 1,000,000 microseconds) between reflows. (Default: 120,000)
Lowering the interval will lower the perceived page loading time but increase the total loading time, especially on slower connections. Values below 100,000 have a significant impact on performance and are not recommended.
First checked in
Has an effect in