1. You can download the SwitchyOmega from the here.
NOTE: Switchyomega for Firefox is currently under Alpha testing.
2. You can either click on proxy or create a New profile
3. Under Protocol choose HTTP. Enter the proxy IP under Server and port under Port.
4. If you are using IP based authentication, you can directly proceed to next step. If you are using user based authentication, click on the lock icon on the right and enter the username and password and click on Save changes.
5. You can add URLs that you do not want to use through the proxy to Bypass List. You can leave it blank if you want to use the proxy for all the websites
6. Now click on Apply changes.
7. Open a New Tab and select the proxy option to use the proxy. You can disable the proxy by selecting [Direct] or [System Proxy].