How can I change proxies in FireFox using "about:config"?

I found an older thread on here that showed how to change proxies in FireFox using about:config but it doesn't work.

I was wondering if any of you guys knew how you can do this?

Configure Internet Proxy settings Mozilla Firefox 1.x
• Select Tools => Options.
• Select the General tab.
• In the "Connections" area click the "Connection Settings" button.
• Select the Manual Proxy Configuration radio button.
• In the necessary proxy field(s), set Proxy Server address (proxy IP) and proxy configuration port.
• Click OK.

I know how to change proxies in the 'options' in FireFox. What I need is to know how I can do it with "about:config".

The reason I need to know how to do this is because I am writing a macro for the iMacro FireFox plugin and need to be able to change the proxy in the address bar, using "about:config".

I suggest you download a firefox addon called autoproxy to manage your proxy changing

I've tried all the proxy related FF plugins. What I need is to know how I can do it with "about:config".

If you know how to search using Google, you wouldn't need to ask such questions here. Do a serach like that given below and read through:

Simple! In Google search box, type:
Please remember to press the "Enter" key.

Google is definitely your best friend in such cases, but you need to go ask it first, the way it understands.
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LOL. I've been all over Google and the boards and I have not been able to find a solution to do what I want to do. I figured I'd ask here.

There is a http://www.blackhatworld.com/blackhat-seo/black-hat-seo-tools/230485-how-change-proxy-imacros-ff-free-plugin.html on here that was talking about what I am talking about, but it does not work.