I ship a lot through FedEx and create the shipping labels on their site. Today I updated to Mavericks and Safari 7.0 and the nightly r157388 of Webkit, both beach ball while trying to fill in the Fedex form when creating a shipping label. Changing to Firefox resolves the issue immediately, also just before I instal Mavericks I used the same nightly and was abel to create labels just fine. There is also a discussion for this in apple support, I have included here the link to it. If one reads through the discussion will find out that not only Fedex, but other sites with forms and JavaScript interaction are affected. The problem can be described the following: All regular pages of Fedex load and are responsive. Once I get to the form for creation of a shipping label, the entire content in the tab freezes. I try to click on a field to type text, or try to click on a drop down menu to select an option, and nothing happens, instead a beach ball comes up and the entire tab is frozen. If one has patience and waits eventually the first operation intended would show, and than beach balling starts again. My take on this is that something must be wrong in the relation between JavaScript, sandboxing of tabs and possibly some security restrictions in Safari 7. But most likely all points to a JavaScrip bug/memory leak/broken loop that slipped into the final Safari 7
Further more on the subject, the same problem occurs on Mountain Lion after updating to Safari 6.1 It was just reported in the apple support thread. It happens with even more sites different form Fedex. I personally did not update to Safari 6.1 and went straight to Mavericks and that's why I was under the impression at first it was related to Mavericks, where the problem has to be searched for in Safari 6.1/7.0
Thread from URL field mentioned that 6.1.1 resolved this issue. So marking this as "RESOLVED CONFIGURATION CHANGED". Thanks!