A few people have pointed out to me that scrolling down pages on perldoc.perl.org was causing their screens to flicker.
Unfortunately I've not been able to reproduce the problem, even when using exactly the same web browser and OS versions. From the reports I've had, it only appears to affect Firefox, only affects a very small number of people, and has nothing to do with CPU power.
However, after some more investigation and help from those affected I think I've found a fix.
The perldoc CSS uses
visibility: hidden; to hide the draggable page index window - this gets changed to
visibility: visible; when the "Show page index" link is clicked.
Today I updated the site to use
display: none; and
display: block; in addition to setting the
visibility property, and according to reports this seems to have solved the problem.
Apologies to those affected, and thank you to Martin von Wittich, Offer Kaye, and Michael Ivanchenko for their help in testing.
Today's update also adds a preferences page which allows you to change the positioning of the navigation bar from Fixed (the default - the nav bar is anchored to the top of the screen) to Standard (nav bar scrolls with the page content).