I like to second the idea of using the FF variant PALEMOON
A fantastic browser.
And for added security add these addons:
, for blocking advertisements on the web.
, See who's tracking your web browsing and block them.
, Remove or manage a new kind of cookies, better known as LSO's.
, Protects against trackers and zombie-cookies
NoScript Security Suite
, Allow active content to run only from sites you trust, and protect yourself against XSS and Clickjacking attacks.
These addon's are not difficult to master and don't cause any slow down (or at least not that I have noticed)
Hope this also helps.