localStorage (and generally any DOMStorage we currently have) can be used to store values that are actually very similar by behavior and exploitation to http cookies. On several places we are missing a way to track these localStorage cookie values and delete them along with http cookies in some cases. This bug tracks these issue. One important distinction: a web site (specified by an URL) can behave as an 'offline web application'. This happens after a page presents it self like that AND user gives that site the 'offline web application' permission to act like that. For sites with this permission localStorage values are no longer considered "localStorage cookies" and therefor for those this bug doesn't apply. This is fixed since Gecko 1.9.2, if I have a correct track here, for sure in the up-to-date Gecko version.