Hi Im just a Macbook user like yourself but I've had my share of problems. I can give you a few ideas if its not fixed, I see your question hasnt been answered.
1. I would remove anti-virus software, a Mac doesnt need it.
2. you could have folder permission problems, just download and reinstall osx or visit apple communities to walk you through creating a new user, bring your files over then delete the old user (your name, home folder) and that fixes everything. Apple Care if you have it will help you with this too.
Get rid of all those cleaning apps, go on youtube and a quick video shows you how easy it is to clean caches and junk by yourself.
3. too many extensions in safari causes problems also, I have many but they are checked off and I only turn on the ones I need by site or by project, except for translation and reload that I keep on all the time.
4. I just love Ghostery as an extention, something to check out if you dont have it Take Control of Your Digital Experience - Ghostery
Make sure to watch the video, more on youtube for the settings. Love it! Tells you everything about the page you are visiting.
Email me if I can better answer specific questions, I'll do my best to help. firstname.lastname@example.org
Flash Player 11.7 is an older version of Flash Player. Could you please try downloading the latest Flash Player 22 from Adobe Flash Player Install for all versions. This should work without any issues. If you are still facing any issues please let us know.