add: runFiltersButton.disabled = !numFiltersSelected; 
context: function updateButtons(){    var numFiltersSelected = gFilterTree.view.selection.count;    var oneFilterSelected = (numFiltersSelected == 1);    // "edit" and "delete" only enabled when one filter selected    editButton.disabled = !oneFilterSelected;    deleteButton.disabled = !oneFilterSelected;    // we can run multiple filters on a folder    // so only disable this UI if no filters are selected    runFiltersButton.disabled = !numFiltersSelected;    runFiltersFolderPickerLabel.disabled = !numFiltersSelected;    runFiltersFolderPicker.disabled = !numFiltersSelected;    // "up" enabled only if one filter selected, and it's not the first    reorderUpButton.disabled = !(oneFilterSelected && gFilterTree.currentIndex > 0);    // "down" enabled only if one filter selected, and it's not the last    reorderDownButton.disabled = !(oneFilterSelected && gFilterTree.currentIndex < gFilterTree.view.rowCount-1);}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/34e5c6a5ac96df343160601fab5d7d61ed1c9deb/FilterListDialog.js/clean/mailnews/base/search/resources/content/FilterListDialog.js