More stable than a stock, a currency doesn't often lose 50% or 80% of its value, unless you have the misfortune to live in Zimbabwe. One of my stocks IMP which is one of the biggest platinum mines in the world did exactly that last year.
Also, you're not going to get a CEO who gets pissed in the company bar and say the wrong thing and the next day the stock is on the floor. I lost money like that.
In fx a 10% move is big. But a block is so expensive and credit so easy to get through margin accounts that people tend to over leverage the trade.
So I think it's more stable than stock, but quite likely you'll over leverage it and get a more volatile equity curve than stocks, where margin accounts are a lot less common.
There is one very big difference though. Stock is 100% predictable where fx 100% unpredictable. A stock will always go up. If it's not going up now, then it will go up later. Unless the company goes bankrupt, the stock will go up eventually. Same is not true for Fx, which is bi-directional. Makes it very difficult to trade...