I have a question about the power of the Proxy settings in Knoppix 4.0.2

When I use Konqueror, I can use Proxy settings. That is working great. With Konqueror I can use several proxies. But, with Firefox, I can only browse with 1 proxy.

If I use control center, I can also change Proxy settings. But, it seems like it's only working with Konqueror. If I add a different proxy to the proxy settings in K Control Center (Internet > Proxy), it seems like it's not working with Firefox and other browsers. Is that true ?

How powerfull are the proxy settings made in K Control Center, is it for the whole Knoppix (also for pinging, mtr etc.), or is it only valuable for Konqueror.