Applies to filemaker Server V13
Does your layout flash with a white screen displaying field and content text only? WebDirect uses two main file types to render your page. UIDL files (User interface description language) and CSS files.
When a WebDirect page loads for the first time UIDL files download and contain the links to the needed style sheets. The page also begins to render. During the time the page has rendered and the CSS files (there are three of them) get downloaded, you will see a white flash.
Mitigating (Sort Of)
I had hoped that by pushing all the CSS up to the top of the three CSS files that are needed for each layout would mean that it is already cached from the first page download.
Here's the problem: WebDirect custom generates 3 CSS files for each layout! Crazy, as the whole Idea if CSS is that you download a master sheet for a site once.
You can reduce the size of the 2nd and 3rd CSS files to a few hundred bytes by making sure all your object styling has been pushed up into a common theme.
This issue will not occur when a user returns to a page because the corresponding pages CSS files have been cached..
To recreate this effect, navigate to another layout, clear browser caches, return to the problem layout..
Addendum: FMP V14
Filemaker's update to V14 now correctly handles CSS and reduces the need for redundant CSS downloads. This small change was a large contributor to the perceived increase in speed.