How do I reset Safari to the default state?

Safari/Preferences/Advanced - enable the Develop menu, then go there and Empty Caches. Quit/reopen Safari and test. Then try Safari/History/Show History and delete all history items. Quit/reopen Safari and test. You can also try try Safari/Clear History and Web Site Data. The down side is it clears all cookies.Doing this may cause some sites to no longer recognize your computer as one that has visited the web site. Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library./Caches/com.apple.Safari/Caches.db and move it to the trash.

Go to Safari Preferences/Extensions and turn all extensions off.

I never had a problem omitting the CustomUserAgent from the code. I always recommend a reboot, just in case.

how to reset safari 8

Open Terminal and enter this command:

defaults delete com.apple.safari

Then restart your computer.

Won't the complete command be

defaults delete com.apple.Safari CustomUserAgent

and could't you just restart Safari after running the command in terminal, no reboot necessary.