My macbook pro has recently become very slow

Question

So this is the details about my macbook pro
Hardware Overview:
  Model Name:          MacBook Pro
  Model Identifier:          MacBookPro9,2
  Processor Name:          Intel Core i7
  Processor Speed:          2.9 GHz
  Number of Processors:          1
  Total Number of Cores:          2
  L2 Cache (per Core):          256 KB
  L3 Cache:          4 MB
  Memory:          8 GB
  Boot ROM Version:          MBP91.00D3.B08
  SMC Version (system):          2.2f44
  Serial Number (system):          C1*******TY4
  Sudden Motion Sensor:
  State:          Enabled
It was running fine until the last couple months when my microsoft office started to act a bit weird. But the speed was still fine until the last few weeks.
I don't very often turn off my mac which I've read to be a problem and that it should be switched off every now and then.
I also have repaired my startup HD and also cleared my disk spaces as suggested.
I've also tried the PRAM option and the OnyX option to give the computer a clean up and maintenance. 
So when i first start up the macbook pro it would run ok with most of the applications i have. I check the CPU usage and its all Ok.
The one thing that takes up all of my CPU usage % is my safari web content. When i watch something on any site or on youtube, the whole macbookpro becomes really slow as all my RAM gets used up by the safari and safari web content. I've never realised how much it is meant to use up but I dont think it is meant to use up that much.
So then after watching something on youtube and such the macbook pro becomes extremely slow and sluggish and will need a restart to run normally
Can I please have some suggestions on what is wrong and how to fix it?
Any help would be greatly appreiated!
<E-mail Edited by Host>

Answer 1

From the Safari menu bar, select
Safari ▹ Preferences ▹ Extensions
Turn all extensions OFF and test. If the problem is resolved, turn extensions back ON and then disable them one or a few at a time until you find the culprit.
If you wish, you may be able to salvage the errant extension by uninstalling and reinstalling it. Its settings will revert to their defaults. If the extension still causes a problem, remove it permanently or refer to its developer for support.