Probably a lot more personal information than anyone would care to have stored in an open, easily accessible manner. This DOM Storage file is one of many so called “supercookies” that most of today’s cleaning utilities fail to remove. Other “supercookies” include identifiable data stored by various Flash, JavaScript, and Java userData methods.
 
Interestingly, Firefox 3.5’s “Private Browsing” information makes no mention as to whether or not it stores data in webappsstore.sqlite, I haven’t verified this, but I would expect it to be explicitly mentioned in the list of “Private Browsing” features.

http://support.mozilla.com/en-US/kb/Private+Browsing

 
 
Luckily, it’s a snap to view the contents with an SQLite viewer, and easy to remove too.
 
I used SQLite Manager for Firefox to view the contents of webappsstore.sqlite:
webappsstore privacy

http://code.google.com/p/sqlite-manager/

 
I guess a better article might be written on the subject of why Bing has stored my actual home address in an insecure, unencrypted, non-cookie format for later retrieval…
 
 

webappsstore.sqlite MozillaZine entry:

Deleting webappsstore.sqlite will delete any data web sites have stored there. A new file will be created when it is needed.

http://kb.mozillazine.org/Webappsstore.sqlite

So removing it shouldn’t be any more harmful than normal cache/cookie removal.
 
 
I’m a fan of CCleaner, but I was surprised to find that it didn’t remove this db file by default. Adding it to the list of files to manually delete is a snap:

C:\Users\xxxx\AppData\Roaming\Mozilla\Firefox\Profiles\xxxxxxxxxx.default\webappsstore.sqlite

ccleaner include files to delete

http://www.ccleaner.com/

 
 

Now where is the option to keep sites from storing data here in the first place?

Well, it appears you can go to about:config and change dom.storage.enabled to false, but the MozillaZine for this option doesn’t detail what other effects this might have.

http://kb.mozillazine.org/Dom.storage.enabled