What is the maximum size of local storage available for Firefox add-ons and/or Chrome extensions?
This isn't standardized, but a Chrome extension is limited to 5 MB unless you ask for extra space: https://developer.chrome.com/extensions/manifest#permissions
You could use this as a rough guide to see if the problem you were trying to solve is appropriate for localStorage. If it's a lot less than 5MB, you're probably okay (though note many browsers don't have full support yet), but if it's more, it's probably the wrong solution.