Error while trying to install safari extensions on Macbook Pro Retina

Question

Dear All,
Yesterday I had to re-install Mountain Lion OS on MacBook Pro Retina. Everything went smoothly however after the installation process and updating sytem to the newest possible version, I am not able to install any Safari extensions. I was trying to find any information in the internet about this but so far I am unsuccessful in solving this issue. I am currently running Mountain Lion 10.8.2 and Safari 6.0.1. I would be grateful for any help.
Best Regards,
Jan

Answer 1

Back up all data now.
This procedure will unlock all your user files (not system files) and reset their ownership and access-control lists to the default. If you've set special values for those attributes on any of your files, they will be reverted. In that case, either stop here, or be prepared to recreate the settings if necessary. If none of this is meaningful to you, you don't need to worry about it.
Step 1
Launch the Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
Drag or copy — do not type — the following line into the Terminal window, then press return:
sudo chflags -R nouchg,nouappnd ~ $TMPDIR.. ; sudo chown -R $UID:20 ~ $_ ; chmod -R -N ~ $_ 2> /dev/null
Be sure to select the whole line by triple-clicking anywhere in it. You'll be prompted for your login password, which won't be displayed when you type it. You may get a one-time warning not to screw up. You don't need to post the warning. If you don’t have a login password, you’ll need to set one before you can run the command.
The command will take a noticeable amount of time to run. Wait for a new line ending in a dollar sign (“$”) to appear, then quit Terminal.
Step 2
Boot into Recovery by holding down the key combination command-R at startup. Release the keys when you see a gray screen with a spinning dial.
When the OS X Utilities screen appears, select Utilities ▹ Terminal from the menu bar. A text window opens.
In the Terminal window, type this:
resetpassword
That's one word with no spaces. Then press return. A Reset Password window opens. You’re not going to reset a password.
Select your boot volume ("Macintosh HD," unless you gave it a different name) if not already selected.
Select your username from the menu labeled Select the user account if not already selected.
Under Reset Home Directory Permissions and ACLs, click the Reset button.
Select  ▹ Restart from the menu bar.