After installing 65 on one of my systems, I noticed a number of user interface elements that didn't look right and for some reason my addon's page just showed blank rectangles where my addons would be, so I thought I'd downgrade to 64. I installed 64 and it seemed successful, but it asked to reboot at the end, which doesn't always happen with upgrades.. but I rebooted and when the system came back up, nothing happened, and my prior Firefox link didn't work anymore. I tried reinstalling 64 again but it said something like the installation was in progress and wanted to reboot again, but again nothing happened. I had to select a new directory for the installation to get it to work.

I thought maybe it was a fluke, so I tried it on another system... and same thing. So is there something unique about version 65 that is making the downgrade fail? What's the right way to downgrade this version?