First, would be helpful if you let us know:
a. The exact Mac model you have.
b. The exact Mac OS are you running.
c. How much free space do you have on your internal drive?
d. Have you been performing any disk cleanup/maintenance at all?
e. Do you make backups to an external device?
f. Do you have either Mac Keeper or CleanMyMac installed on your machine? If you do, get rid of them right away!
Now, it would be prudent to disable Flash Player. I did that a couple of months ago for Google Chrome (that is the browser I use 99.9% of the time), and I have not missed it at all. This link talks about Flash Player, and how to disable it:
http://www.tomsguide.com/us/disable-flash-how-to,news-21335.html
Also, the use of Flash Player has been known to open up your system to malware and adware, which can slow things down considerably. You can use the excellent freeware tool Malwarebytes Anti-Malware. You can get it from here:
https://www.malwarebytes.org/antimalware/mac/