I haven't done many for CF, but they have treated me really well. They sent me a nice thank you email after the first batch I did. What I like are their rewards plus they approve within 24 hours. I remember doing one of their 25c HITs in a minute and then I spent more time trying to figure out what was the "catch". I satisfied myself there wasn't any and did a bunch more. Too bad they don't have more work available, but I suppose they would cut their rates like the rest of them.
Be very careful of these hits. I too thought that they were an easy "go to" until he mass rejected me and brought my stats down quite a bit. I'll never do hits for them again. Besides they are only paying less than $1 per hour.
For FF, yuo may have to install the grease monkey add-on first. Chrome might work for yuo, but it isn't for me. Chrome started blocking all scripts that aren't available on google play on 8/1. I saw a work around posted here somewhere, but it didn't work for me.