The Firefox web browser like any other modern web browsers uses IndexedDB to store persistent data that is associated with the browsing profile.
A report on German computer magazine Heise suggests that Firefox's handling of the storage may impact user privacy on the Internet.
While Firefox users have several tools at their disposal to manage the data, it has two deficiencies when it comes to the handling of IndexedDB data.
First, that the clearing of browsing data does not touch the data, and second, that Firefox users have little control when it comes to allowing or denying sites the right to save data in the first place.
Update: Mozilla plans to correct the issue that clearing the browsing data does not clear IndexedDB data with the release of Firefox 56.
Firefox users have two main options currently when it comes to IndexedDB data. They may use Page Info to clear the storage, or the Firefox Developer Tools.
A right-click on any web page and the selection of Page Info opens the configuration window. It highlights if the domain has saved data to the local system, and how much.
The clear storage button works, but it will only clear the data for that particular site. The options to set the process to "always ask" or "block" don't work properly however, and are reset automatically when Firefox is restarted.
The about:preferences#privacy setting "Tell you when a website asks to store data for offline use" does not work either" when it comes to this type of storage.
Page Info's permissions page has little use when it comes to managing local data, as it lists data only for the active domain.
The Firefox Developer Tools improve this slightly; the data that is stored in the database is listed by the browser's Developer Tools, but again only for the selected domain.
Press F12 to open the Developer Tools, and select Storage when the interface opens. If you don't see storage, click on settings and enable storage there first. You can delete entries individually there, or all at once.
The best option right now to find out which sites use the offline storage is the following one:
You can delete some or all of the folders there to clear the storage.
Firefox has an option to disable IndexedDB completely. Doing so may cause incompatibility issues with some websites.
A value of true means that IndexedDB is enabled, a value of false that it is turned off.
Heise notes that the issue was first reported eight years ago to Mozilla.
Firefox 57 will improve the manageability of site data. It features a new Site Data entry under about:preferences#privacy which you may use to clear all data, and to manage data from sites that used the feature in the past.
This improves the management of persistent storage in Firefox, but it does not address the issue that site data is not deleted when the Firefox browsing history is deleted, nor that the permission system seems broken when it comes to persistent data.
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