If Spotflux (regular, not Lite) is installed on your system and sets itself as your default connection method in your Windows Internet Options, LAN settings, then Firefox and all of your other software that connects to the internet will use it by default. According to their help page:

"Unlike a Proxy, Spotflux works on your entire internet connection, not just browsers or applications that need to be been manually configured to a Proxy to function." Source: http://www.spotflux.com/learnmore.php#questions

So it sounds like you do not need an add-on to use Spotflux, unless you want to limit it to one application at a time. Currently it seems they are only offering an application-specific add-on for Chrome.

In response to your main question, I don't have any particular recommendations for proxy or private VPN services.

Thanks for the reply jscher2000. I used to use Spotflux regular but had too much trouble with it so I switched to lite. I thought it worked as my default connection method like the regular. When I searched for my ip address when using Firefox I got my real address. When I used Chrome I got a good vpn address other than my own. So that clears it up, it apparently is browser specific but not for Firefox. Thanks again.

If you want Spotflux to create a Lite add-on for Firefox, feel free to let them know. :-)