Adobe Flash Player is an extremely necessary tool when browsing the internet. It enables your web browser to view files encoded in the Flash format, which includes almost anything that is streaming (especially YouTube). To install Flash Player on a computer the normal way, you must have administrator rights on your system. If you do not, it can still be installed, it'll just take a few extra steps.
Download the archived Flash Player plugin from the Adobe Flash website. Download the plugin to a location on your hard drive where you'll be able to find it. The file will have a .XPI file extension.
Change the .XPI file extension to read .ZIP. You can do this by right clicking the file, selecting "Rename" from the options and changing the part of the file name after the period.
Extract the two files contained in the archive. You can do this by right clicking on the .ZIP file and selecting "Extract" from the list of choices. This will extract them to the directory the .ZIP file was located in.
Copy the two files you've just extracted to your web browser's plugins folder. For Mozilla Firefox, the folder is in the Program Files/Mozilla/Plugins folder. For internet Explorer, it is in the Program Files/internet Explorer/Plugins folder.
Restart your web browser. To finalise the changes you've just made, close out of your web browser and relaunch it. After it loads, you can enjoy the Flash player.