automatically change firefox proxies when they go down

I'm trying to find out if anyone knows of a way to automatically change out a bad proxy in firefox.

Say like a proxy dies, and i want to change it too a new one what is the best way? is there some way to do it automatically?

thanks

not any easy, ready-made solution, at least not any i know of

maybe with imacros somehow
i'm thinking about making a .csv file with the proxies, one proxy per line , specify this .csv as datasource and record a macro of checking the proxies against basically any site in a given timeframe set by you (every minute, every 5 minutes etc.), if the page loads/a certain html element is found before timeout (which is also set by you), keep the proxy, if not, skip to the next one
play the macro in loop