Shared components used by Firefox and other Mozilla software, including handling of Web content; Gecko, HTML, CSS, layout, DOM, scripts, images, networking, etc. Issues with web page layout probably go here, while Firefox user interface issues belong in the Firefox product. (More info)
We have the information there are no localStorage data for an origin (scope). It's easy to pronounce a DOMStorageCache as 'loaded' with no data quickly during it's creation so that access to it will not block at all.