If you're having problems with Firefox, refreshing it can help. The refresh feature fixes many issues by restoring Firefox to its default state while saving your essential information like bookmarks, passwords, and open tabs. 

What does the refresh feature do?

All of your Firefox settings and personal information are stored in a profile folder. The refresh feature works by creating a new profile folder for you while saving your important data.

Add-ons which are normally stored inside the Firefox profile folder, such as extensions and themes, will be removed. Add-ons stored in other locations, such as plugins, will not be removed but any modified preferences (such as plugins you have disabled) will be reset.

Firefox will save these items: 
  • Bookmarks
  • Browsing and download history
  • Passwords 
  • Open windows and tabs
  • Cookies 
  • Web form auto-fill information 
  • Personal dictionary

These items and settings will be removed:

Extensions and themes, website permissions, modified preferences, added search engines, DOM storage, security certificate and device settings, download actions, plugin settings, toolbar customizations, user styles and social features will be removed. 

Please, take help first, and then do it now. 
Open new Tab, and type 
Press Enter, click on "Refresh Firefox...." at top right corner