Was not sure to post this.. but actually came across this a week ago while testing OS X 10.9 GM version. It you try to open a webpage via the script step "Open URL". it does not work with safari. You do not get any error.. it just refreshes the current page. Probably has something to do with new security/permission rules..

 

Probably will have to add "FileMaker" into the "Allow Apps to control computer", security settings..

FM has posted FM12v5 for Mavericks compatibility:

 

http://help.filemaker.com/app/answers/detail/a_id/12487

Yes, I have installed FM Pro 12.0v5. Same issue. Need to update my profile..

I haven't experienced what you are saying. Can you post a copy, or mockup, of the file?

Lee, I am not sure what happened. I had created a simple layout the you could paste the URL into and a button to open it, and a script version of the same thing and neither of them were working. I did not have another machine set up the same way to verify, but could verify that the machines with OS X 10.8.5 were still working. I don't know what may have changed since yesterday other than maybe a re-booting after applying the FM 12.0v5 update. But in testing now, both ways are now working correctly..