Quick Start or Fast Start is one adware that can be very annoying in any browser. Here are steps on how to remove it :
Step 1 :
Go Tools/Add-ons and in Extensions remove Fast Start or QuickStart adware
Step 2 :
Now we need to remove chrome://quick_start/content/index.html from the Firefox browser tab.
Write in Mozilla in search : about: config
Then type in search: browser—new tab.URL and find this preference.
Change it to about: new tab
The problem is solved.