2011 MacBook running El Capitan 10.11.6 was crashing a lot when using Firefox, and I was running Disk Utility First Aid a lot, without a lot of improvement. It also showed that in the graph that half of my hard disk was filled with unspecified who knows what. After running Disk Cleaner, only about 1 GB was cleaned off my hard drive — I was hoping a lot more would be cleaned. While typing this, I got a Java Update pop up, and I installed that. I’ll update this review as developments warrent after I’ve used my MacBook a while. But out of the gate, I can say Disk Cleaner was very easy to use.