This is the method I used. I didn’t feel like paying for Clockworkmod tether, so I found a solution that is almost identical, with alternate software.

No root needed

I’ve tested this with my Nexus 5 running 4.4.2

The problem:
Using the stock tethering method, only redirects you to the T-Mobile page where they advertise their tethering option. By default you can’t access any other internet site.

How they do this:
T-Mobile counts the hops to their servers using the TTL function, if an extra hop appears, T-Mobile will assume you are tethering without permission.

On your phone:
Get Proxoid
Go into your settings>More>Tethering & Portable hotstpot, check the box that says “Portable Wi-Fi Hotspot”
Take note of the Wi-Fi password
Open Proxoid and check the ‘Start’ box

On your computer:
Connect to the Wi-Fi Network, and enter the password noted previously
Open a command prompt and type ipconfig
Look for the default gateway for your current Wi-Fi adapter (usually 192.168.43.1)
Take note of this IP address

Checking if the connection works:
In command prompt type ping (ip address)
e.g. ‘ping 192.168.43.1’
The response should not time out
Close the window

For firefox:
Go into Settings>Network under connections, click “settings”
Select manual proxy configuration
In HTTP proxy, Address: (IP noted earlier) Port: 8080
Check the box that says “Use this proxy server for all protocols”
Click OK

Your tethering is now configured