Proxy is not changing after switching

I have some socks proxies. FoxyProxy (FP) works fine when I choose "A" proxy first time. But when I switch to another "B", nothing changes. FF still uses "A".
I tried to disable FP (direct connection, default FF settings), and choose "B" again. But it still uses "A".
For tests I was using http://www.lagado.com/proxy-test
What did I miss?

Please read Why does

Thanks for explaining!

Thanks for explaining!