Adobe Flash Player is a well-known route for nasty stuff to get onto your computer but
(a) it's safe enough if you ensure that it's up to date ; and
(b) you need Flash to view many websites containing videos. (Although many sites, including Youtube, are now switching over to using HTML5, Flash continues to be the main way of offering video content across millions of websites).
So my recommendation is to keep Flash but to ensure that it's up to date.
Go here
https://get.adobe.com/flashplayer/
Deselect the 'optional offers'.
Click 'Install Now' to download the file.
Click the 'Downloads' button in your browser. (In Firefox it's a downward-pointing blue arrow at the top right of your screen).
Double-click on file name to run the installation process.
Close, and then re-open, your browser.
(If you don't change the default setting in the installation process, Adobe Flash Player will automatically update itself in future).