iMac Safari web browser
You need to reset Safari's preferences.


Click on “Safari” located in the menu bar in the top left hand
corner of the screen
Click on “Reset Safari...”
Place a checkmark beside all available options
Press the “Reset” button


If you arent able to reset Safari then you'll have to manually remove some files.


Click on the Hard Drive icon located on the desktop
Browse to “Users > (Users Home) > Library > Safari folder”
Drag every file except “Bookmarks.plist” into the Trash
Browse to “User > (Users Home) > Library > Preferences”
Locate “com.apple.Safari.plist”,
“com.apple.internetconfigpriv.plist” and
“com.apple.internetconfig.plist” and drag them to the trash.
NOTE: If “com.apple.internetconfigpriv.plist” does not exist, 
ignore it and just trash the other two files
Restart Safari