Q: what to do when system running slow

Not enough free space on the startup disk can slow the system down.

Right or control click the MacintoshHD icon on your Desktop.

Click Get Info. In the Get Info window you will see Capacity and Available.

Make sure there's a minimum of 15% free disk space.

OSX Tips Where did my Disk Space go?

Avoid so called Mac cleaning utilities. Your Mac runs maintenance in the background for you.

Mac OS X: About background maintenance tasks

As for Safari. Try resetting. From the Safari menu bar top of your screen click Safari > Reset Safari

Select the top 6 boxes then click Reset.

Quit then relaunch Safari to test.