Why is CCleaner erasing IE temp internet files?

CCleaner for Windows
1

The only web browser I use is Firefox. But when I run CCleaner, it usually erases numerous files located in the Microsoft Internet Explorer (IE) cache (Temporary Internet Files), in addition to the Firefox Internet cache. Since I never use the IE browser, why does it contain any cache files?

Thanks for any info.

2

Even if you don't use IE, Windows and other apps use it.