What is the browser "session"?
One of the things CCleaner cleans is the "session" in various browsers.
Now, I tend to use Chrome or Firefox. I just ran Ccleaner when I had several tabs open in each. After runing CCleaner, no tabs. Does CCleaner wipe these out?
If you run analyse - for sessions only, look at the detailed results, and maybe right click and go to folder, then you will see that these are mainly log, bak, and other recovery files for that particular browser
So yes these are the files that have info on what tabs were open when the browser last closed (for whatever reason).