firefox proxy settings via command line

The proxy setting is stored in the user's prefs.js file in their Firefox profile.

The path to the Firefox profile directory and the file is:

%APPDATA%\Mozilla\Firefox\Profiles\7b9ja6xv.default\prefs.js

where "7b9ja6xv" is a random string. However, the directory of the default profile always ends in ".default". Most of the time there will be only one profile anyway.

Setting you are after are named "network.proxy.http" and "network.proxy.http_port".

Now it depends on what technology you are able/prepared to use to change the file.

P.S.: If this is about changing the proxy settings of a group of users via the logon script or similar, I recommend looking into the possibility of using the automatic proxy discovery (WPAD) mechanism. You would never have to change proxy configuration on a user machine again.

I don't think you can. What you can do, however, is create different profiles for each proxy setting, and use the following command to switch between profiles when running Firefox:

firefox -no-remote -P <profilename>