Some sites still require Adobe Flash Player, most do not. Over the years, Flash Player has increasingly become a weak spot in a systems security. Namely, zero day attacks, that Adobe doesn't seem to deal with, fast enough.
Most browsers are slowly moving away from both Java and Flash. Whether you need these plugins or not, only you can answer. I would advise finding ways around needing them, assuming you still do.
I have spent 2016 Java and Flash free. A very small number of off the wall websites, no longer work for me. I don't seem to need those websites.
If you do decide you need Adobe Flash player, make sure it is always up-to-date. IMO and the opinions of browser designers...it isn't worth the risk.
https://blog.mozilla.org/futurereleases/2016/07/20/reducing-adobe-flash-usage-in-firefox/Quote
We continue to work closely with Adobe to deliver the best possible Flash experience for our users. Our engineering partnership has led to improvements in high-DPI support on Windows, enhanced sandboxing, and an accelerated Flash rendering pipeline that improves performance and stability.
These changes are part of our ongoing efforts to make browsing safer and faster without sacrificing the Web experiences our users love. As we announced last year, Firefox plans to drop support for all NPAPI plugins, except Flash, in March 2017. The next major Firefox ESR (Extended Support Release) release, also scheduled for March, will continue to support plugins such as Silverlight and Java until early 2018, for those users who need more time for their transition.