You're not crazy. I was having the exact same problems. Same OSX and Safari versions as you have, although I use Firefox 99% of the time. I found a direct download link for Flash: Installation problems | Flash Player | Mac (hopefully you can see the link - I pasted it in as text, but the page made a hyperlink out of it). I downloaded the .dmg and opened it on my desktop, which gave me the "Install Flash".app. But here's the difference this time: I CLOSED FIREFOX before running the .app. It had been failing on me through several different update cycles, but this time it installed correctly! I then went to the Apple icon and System Preferences. Double clicking on the Flash icon shows me that I now have 14.0.0.176 (I had 14.0.0.145 before updating), so I guess I'm good for the moment. Hope that helps.
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