To install Flash: (You have to have a Flash compatible browser in order to install Flash. You can't install it under Silk.)
Do the following on the Fire/Fire HD itself:
Swipe down from the top > More > Device > Allow Installation of Applications.
Install ES File Explorer: ES File Explorer
Download and install the Dolphin HD and Flash Player apk files from this link:
https://www.dropbox.com/sh/9d8gxh75f0747f1/83fV5m6x2c
Once both files are downloaded to your Fire, open ES File Explorer and look in the "Downloads" folder. You should see both files there. Install Dolphin HD *first* by tapping on the icon. Then install Flash.