There is a regression in r54122. The last build I used last week was r53845 and it was working ok. I don't know if the regression is in any of the builds in between. Basically it presents with the official Fedex page (but you need to have an account with them in order to be able to create a shipping label). Although Fedex uses for many things Flash, it seems for the form in question they use pure javascript. The form loads, and when done they seem to keep in a variable the address book and the shipping profiles, so those are suggested when typing in the fields of the form. Today after updating to r54122 the page loads, but it never finishes, it seems completely unresponsive, with the clock showing, it can not finish loading. Even clicking on the logout link won't work, also nothing is suggested in the fields when trying to type, it seems something is breaking javascript procedures being unable to put all variables in memory I think. I cleaned caches and such but no result. Reverted to the older known working build r53845 and all is back to normal. Also Firefox latest beta works without any problems. So it is definitely something broken in the build(s) after r53845 Find attached the source code of the Fedex page. I only deleted most of the address book and the profiles for privacy and left only 1st entry of those to be easy to understand the structure they use.
Created attachment 47846 [details] Source of Fedex page
<rdar://problem/7602671>
Ok, the new nightly build r54267 fixes the issue. All works as expected again.