[Entire Drive (All data will be erased)]

When it says "Entire Drive (All data will be erased)" does it mean only what was added after windows, or does it erase the whole hard drive?

 

What exactly does it mean by "data?" Does it include the operating system?

[Firefox Address Suggestions won't Disappear]

When I type into the Firefox address bar, a few websites keep automatically being suggested. It is always the same ones, even though a few I never visited, though maybe another user visited those sites.

 

I tried everything within Firefox such as delete history, the privacy options, etc.

 

I bought CCleaner Professional, used it, but the CCleaner Professional will not remove it.

 

How do I get CCleaner to work, please?