Why I can't clear the filters' cookies of the plugin grid filter

hello,everyone,

I written a gridpanel with the plugin of gridfilter.
(http://extjs.com/forum/showthread.php?t=14503)

After finished,the filter act.

But,the filters didn't disappear in any condition,even when I refreshed the page,or restart the IE/Firefox.

Anybody knows how to delete the cookies?

The page includes all the filters' files:
ext-all.css
ext-base.js
ext-all.js
EditableItem.js
RangeMenu.js
GridFilters.js
Filter.js
StringFilter.js
DateFilter.js
ListFilter.js
NumericFilter.js
BooleanFilter.js


And It also has this line :
Ext.state.Manager.setProvider(new Ext.state.CookieProvider());

Can anybody help me to solve it?