My Gmail Inbox messages are now double-spaced

For 3 days now, I am noticing my gmail inbox page messages are double spaced when they were single spaced before, I don't know what caused this but obviously, something I may have clicked inadvertently. I used to see this before also but it would correct itself to having my messages lining up as single spaced.

I have not yet converted to chrome and am using the old standard gmail.

Just looks weird that the lines are far apart. I want them back to single space, anyone know how to do this? And step-by-step instructions only please, if you can.

Thank you.