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I really appreciate the time you take to reply BUT few of us are as fastidious as you are. The computer is there to serve us and not the other way round.
Once again please let me know how I can uninstall apple updates to see if these created the problem in the first place.

It's not a matter of being fastidious. It's a matter to being proactive to avoid issues. Would you take the same approach for an automobile, ie, the vehicle is there to serve you, and you not it? That's spells disaster. The better approach would be that both serve each other, and I can tell you that by following that credo, automobiles and computers have served me well (as has other stuff).

Now, it's unfortunate that these issues are still there, and it looks like trying to fix the issues without doing any further disk maintenance is not going to work. Trying to find any updates you have done (unless you remember specifically which ones you did) is almost like trying to find a needle in a haystack.

One other thing is possibly apparent. Given that your iMac is 8 years old, there is a chance your internal hard drive is going bad. I'm not saying that is definitely the case, but it's possible.

Here are a couple of more suggestions:

1. Quick and "dirty" - try using another browser and see how it reacts. Firefox (https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac), Google Chrome (https://www.google.com/chrome/browser/desktop/), or Opera (http://www.opera.com/computer/mac) are good choices. Crome will the fastest.

2. Longer term fix - 1) Invest in an external drive. 2) Erase and format that external drive with Disk Utility. 3) Make a backup of your "system" to that external drive (Time Machine is OK< but SuperDuper! would be better). 4) Boot your Mac in an "external" manner. If you use SuperDuper! for your backup, you can boot from it. Otherwise, you'll need to boot to the (hidden) Recovery HD partition (this link discusses that: https://support.apple.com/en-us/HT201314). 5) No matter how you boot externally, use Disk Utility there to Erase and Format your internal drive, and then do a clean, fresh, "virgin" installation of Yosemite onto your internal drive. (You'll need the file "Install OS X Yosemite", which you cam get from the App Store (should be contained within your "Purchases"). Note that will also give you a fresh, "clean" version of Safari.
6) Reboot your iMac, and see how things are. If everything is better, then there is something else on your system that is causing problems. At that stage, it is on your backup.