Reset Firefox to Default State - Fix Most Problems

Reset Firefox to Default State - Fix Most Problems:

1. Click the menu button and then click help.
2. From the Help menu choose Troubleshooting Information. 

Note:
If you're unable to access the Help menu, type about:support in your address bar to bring up the Troubleshooting Information page. 

3. Click the Reset Firefox… button in the upper-right corner of the Troubleshooting Information page. 





4. To continue, click Reset Firefox in the confirmation window that opens.

5. Firefox will close and be reset. When it's done, a window will list the information that was imported. Click Finish and Firefox will open. 

Firefox will save these things:

Bookmarks
Browsing history
Passwords
Open windows, tabs and tab groups
Cookies
Web form auto-fill information
Personal dictionary

These items and settings will be removed:

Extensions and themes
Website-specific preferences
Search engines
Download history
DOM storage
Security settings
Download actions
Plugin settings
Toolbar customizations
User styles and social features