In practice there are limits, it would be very rude to let random websites fill your entire disk until you manually clear the storage. This page tests how much

In practice there are limits, it would be very rude to let random websites fill your entire disk until you manually clear the storage. This page tests how much you can store in practice, the current versions of Chrome and Firefox both seem to barf after storing just 10MB: https://arty.name/localstorage.html https://arty.name/localstorage.html . What I meant by a persistent data permission is adding an explicit permission prompt which allows an app to bypass that limit and store any amount of data, if the user allows it, which you can't currently do.