Writing to the disk - infected?

: Function ereg_replace() is deprecated in /mozdev/sandbox/php/include/globals.h on line 95.

My security software tells me tha FoxyProxy Plus is writing to the disk!
Is my security software wrng?

Hi,   FoxyProxy writes to

Hi,
 
FoxyProxy writes to disk to save your settings. It writes to a file called foxyproxy.xml in your Firefox profile directory.
 
Eric