64 bit browsers not running right on 64 bit system

I am having severe problems with Windows 7 Home Premium 64 bit ,on my Toshiba satellite C870-11H laptop.
It has become more slow and erratic, espesially when using browsers and Windows notepad.
I get long delays when addind new tabs or searching online.
I have tried
IE11, Firefox, Google Chrome, Pale Moon, and Opera all with the same results
All versions were 64 bit.
Apart from when using the above and Windows Notepad, the laptop behaves itself.

I have performed all the recommended solutions,ie full AV scan (Kaspersky TotalSecurity, ADWCleaner, Spybot Search and Destroy, with no infections found.
I have run sfc /scannow, and CHKDSK with no problem.

Just as a test I removed all the browsers, and just installed Pale Moon 64 bit.

The problem remained, but when I replaced PM 64 bit with the 32 bit version,all the slowness disappeared.
(Notepad still plays up though)
The Laptop has 8GB of memory, and plenty of HDD free space.

So it seems that 64 bit browsers are the problem, but I can't see why.

Any ideas anyone?

There may be a buggy 64-bit script running in the background, whenever you are running a 64-bit browser. And possibly the equivalent 32-bit version of that script, which runs when you are running a 32-bit browser, is not buggy. Or maybe that script runs better with a 32-bit browser.

That's all I can think of.

Thanks for quick reply. How do I check if any scripts are running? Do you think I should run Noscript, if so how can I identify/view buggy scripts. Windows Notepad is still very sluggish, could this be a script problem? I think I may try a repair install of Windows 7 if I can find a genuine install disc, as laptop has OEM version so I can't download an iso from MS.

There may be a misbehaving program or service which loads whenever you start Windows. To see if that is happening, and to see how to fix it, check my post here:

Strange Problem: Windows 7 64-bit booting up slow all of a sudden...

Thanks for all your help, I think I have fixed it.
I tried the ideas suggested, disabling all services (apart from ms ones) in msconfig, but there was no improvement.
So I thought I'd give Malwarebytes a try.
I downloaded the latest version from their website, but when I clicked on install, I got a "The setup file is corrupted, please download again" message.
After trying various other download sites with the same message, and downloading with a different computer onto a USB stick, I was very suspicious that something was preventing the installation. So a web search led me to the Chameleon version of the program,from the Malwarebytes website.
This is designed to fool any malware that tries to interfere with the program installation/running.
I downloaded this and ran it according to the helpfile instructions, and got it to install.
A scan then revealed 834 various PUPs and BHOs,which after quarantining and rebooting the computer, and loading the latest Firefox 64 bit browser, seems to have done the trick.
I re-enabled all the services in msconfig, and all seems well again.
Once again,thanks for your help,it is easier when you Know there are people willing to help you.