How to delete all Safari Plugin's, Addons, Extras and so on...

I use none of those things. All I can suggest is that you uninstall them. AFAIK, they're available for all accounts, so creating a new one won't help. However, if it does help, then I suspect corruption or conflicts within the original. If that's the case, when logged into a new admin user account, backup the bad account's folder, delete the bad account, selecting the save data option, recreate the bad account using the same username/password combo, log out and back into the recreated original account. If the problem's solved, open the saved data dmg file in /Users/Deleted Users/, open the /Library/Preferences/ folder from the saved data, open the current /Users/restored account/Library/Preferences/ folder, and slowly copy plist files from the saved data folder to the current one that don't exist in it. Log out and back in to ensure there's no conflict and things still work correctly. Resolving conflicts or identifying corrupt plist files is a laborious process. Good luck.

See http://discussions.apple.com/thread.jspa?messageID=4703015 for more details on this process.

There's also that "Reset Safari" menu option in the Safari menu on the top left of the screen. Takes a few seconds to dump all the settings and plugins and everything, but it generally does the job.

Good luck getting everything running right 🙂

Try looking in:
~/Library/Safari/
or
~/Library/Application Support/

You can also try to delete
~/Library/Preferences/com.apple.safari.plist

Most are stored in ~/Library/Internet Plug-Ins and /Library/Internet Plug-Ins