I've been dealing with "white flash" with FF and IE for some time. I run HIGH CONTRAST graphics ie, reverse to White Text on Black background, all applications and use, all animation, and all js killed BECAUSE I am gradually going blind. Accessibility Mode on steroids. (Note: might try it, the web has a different and more personal look and all that freakin' noise disappears, too!)
In the process of dealing with that white flash problem many experiments and explorations occurred. My tinkering as well as everything I could find on Bing and, for me, desperation make me click and test EVERY function/option in FF. And I found it. There is a solution to not only the WHITE FLASH between pages that many experience, but the SLOW LOAD of posted replies at WW.
If you are having this slow post at WW problem test it yourself. It works for me. Just passing it along.
(Makes sense. These days, with all the third party crammed on some sites the auto refresh is working over time and the browser, with no content yet in hand, will display a white screen. Further research indicates that some sites ... unnamed but major sites ... have as many as 85 auto refresh before a single letter or image is displayed. Don't take my word for it, test it yourself.)