Adobe Flash player continues to get the cold shoulder from major computer makers and their browsers. Flash has a couple of problems; it's a widely-installed method of allowing your web browser to display video and sound, but unfortunately it's also an equally popular target as a method of distributing malware.
Regardless of how frequently Flash player is patched, more security vulnerabilities pop up. Computer companies want to try and steer us away from Flash and on to new technologies like HTML 5. To this end, Apple is making the next version of their Safari browser block Flash by default, along with several other possibly troublesome plugins, like Oracle's Java.
Starting with Safari 10 in macOS Sierra, Safari will begin blocking Flash across all websites even if you have the plug-in installed, requiring users to activate Flash on a page by page basis. Users can chose to activate only once (this is the default option) or every time. If you visit a website that has Flash and HTML5, Safari will automatically opt for the latter.