On January I've launched my app in Chrome store (place for Chrome extensions). At the same time I added it into similar place for Firefox Addons. I told my friends who were developers to use my tool. Got pretty good feedback on it.
But since then I really had no clue how to go further with this app.
I was adding slowly some features, but not really caring about numbers of users. Tbh I'm not the best in terms of marketing.