ProxMate was one of the few remaining free proxy browser extensions, but earlier this month, it moved to a subscription model (along with receiving a new icon and facelift). So, if you want to continue using ProxMate, you'll have to cough up some coin.
So, that's the bad news. The good news is that ProxMate is currently offering a substantial discount on its regular prices (well, what will be its regular prices):
Alternatively, it might be time to investigate some other options, though the pool of free choices is getting shallower by the day.