You can’t access the hidden wiki just using a common browser like firefox or google chrome, but you need firefox so if you don’t already have firefox download and install it.
Then you should download the Tor Browser, click here to download it
When the download is complete, double click the downloaded file choose the destination folder (the folder where you want to extract tor browser) and choose extract . Then open the folder where you extracted tor browser and double click “Start Tor Browser”
Firefox will open up using this as the home page
From there, you’re now at some level anonymous and you are able to gain access to .onion and the hidden wiki !
The Final step to access the hidden wiki is to paste this url to tor browser: http://zqktlwi4fecvo6ri.onion/wiki/
UPDATE 24/08/13: The Hidden Wiki seems to be down, if rumors in forums are true, the admin of the hidden wiki just got arrested. You can use these mirrors of thehiddenwiki:
The content of this Web site is provided for informational purposes only
I am not affiliated in any way, shape, or form with the hidden web, and I do not acquire any kind of responsibility for anything that outcomes through following these guidelines (positive or negative). You are following these guidelines at your own risk