how to disable adds from firefox browser

hi,

At the top of the Firefox window, click on the Firefox buttonOn the menu bar, click on the Tools menuAt the top of the Firefox window, click on the Tools menu, and then click Add-ons. ...
In the Add-ons Manager tab, select the Extensions or Appearance panel.
Select the add-on you wish to remove.
Click the Remove button

also please see the below link.

https://support.mozilla.org/en-US/kb/disable-or-remove-add-ons

Here is your problem: the ad Findbestdeal:

You have to remove it.
Here are some examples:
http://malwaretips.com/blogs/findbestdeal-virus-removal/
https://www.system-tips.net/remove-findbestdeal-pop-ups-adware/
https://www.how-to-remove.com/findbestdeal/

There is a great free addon for Firefox called NOSCRIPT

It stops clickjacking etc., even stops many adverts on trustworthy websites.
When you install it, every time you visit a website for the first time, you have to allow it.

It won't fix your present problem but will help avoid problems in the future.
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(By the way, when removing malware, you will always get better results if you do so in SAFE MODE)

If you want to keep the toolbar or whatever it is you have installed on your browser, AdBlock is the best option out there. But seriously, run some anti-malware software.

Thanks to all for ur  valuable suggestions

thank you...
and good luck to all of us as Windows O/S and all the various "desired" browsers try to work together.