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Hello, had the same problem.
Using Safari 7.0.5 with OSX 10.9.4
This remedied the problem.
Click 'Safari' - 'preferences' - 'advanced' and make sure 'Show develop in menu bar' is checked
When on the offending download page
Click 'Develop' - 'Disable styles'
Scroll down and click 'Install now'
This will take you to the next page and the download will start
Click 'Develop' and uncheck 'Disable Styles' when the download is complete
Reload the page
The page will now be displayed correctly and finally we can install Flash...!
Someone should fix this methinks!?!