Temporary IE files when using Disk Clean

Hi, all, 

 

Not a problem as such, but I'm curious as to why this happens.  I clean up my registry and C: drive regularly using the tools in Norton Utilities (V14).  Every time I do, it finds tempoary Internet Explorer files, the last time over 1000 entries.  Since I use Firefox for net access, I wonder why this is, especially as I don't always get temporary files deleted from Firefox.

 

Thanks,

 

Ian