Open Radar

 
Summary:
Since updating to Mavericks, Safari has stopped working correctly on certain sites, Facebook and Pinterest being two major sites. It seems that Javascript (and maybe CSS) isn't executing (or isn't executing completely) unless triggered by an unrelated event such as using Mission Control.

Steps to Reproduce:
Open a browser tab, load Pinterest.com, mouse over any pins and see that no hover items (like, repin, etc.) show up. You also can't click to expand a pin. Also, scroll to the bottom of the page, the infinite scrolling doesn't work.

Next, activate Mission Control and simply return to Safari, now hover states work and infinite scrolling loaded the next page, but you have to enter Mission Control again to get the third page, and so on.

The same is true for Facebook.com. Infinite scrolling only loads each page after entering and exiting Mission Control.

Expected Results:
These tasks (rollovers, infinite scrolling, etc.) should just work based on their respective triggers. No outside trigger (i.e. Mission Control) should be required.

Actual Results:
I will attach a video file of the bug in action, but the actual results are described above.

Regression:
Restarting the computer solves the problem temporarily. But eventually Safari enters a state where this starts occurring. Once it does, there is no fix I've found other than restarting (possibly logging out/in, but haven't tried). Simply restarting Safari does not fix the problem.

Notes:
Provide additional information, such as references to related problems, workarounds and relevant attachments.