I accidentally came across the CryptoTab for the Chrome browser recently. I wasn't too sure that it wasn't all a bit too good to be true. Turns out that it is a legitimate thing, but... it's horrendously slow.
The way I understand it, it essentially mines using your spare processing speed while the browser is open. Where the thing's strength is though is in your referral network. People are making reasonable amounts of cash provided that their referral network is reasonably strong.
You get a percentage based on about 10 levels of ACTIVE referrals. It won't do you much good if your downlines are online for an hour or two a day. I'm the perfect candidate for a referral because my system is running 24/7 ( I work from home, so I can also leave the laptop on while I'm out etc). Not too bad for a passive type affair. Your referrals also appear to get bonuses from the "originator". So everyone is really helping everyone else.
I've paired it with a Luno wallet for convenience. A major plus is that a) it doesn't cost you anything per se b)the tab has options for quite a few different browsers(there is even something for the Android system) like Firefox.
If anyone hasn't actually got this little extension yet, feel free to use my link and build the network further.