Easiest browser technology that can do the following task
 

Wanting to use a browser offline and have it load a local file (.html or .asp or ...) where the file contains scripts written in a language that is yet to determined.

The scripts read items in a todo list stored locally in a format that is yet to be determined.

The scripts facilitate editing individual items, or changing the order of the items instantly. For example you press Control-Up and the selected item goes one position up.

Can this be done with just cookies and javascript?

Other ideas how to do it?

This must work on PC's and old symbian smartphones like the Nokia E71 and future blackberry smartphones. Maybe android ones too. Therefore an SQL database would rather be avoided if possible, unless it works in all the above platforms.

Crucial: it must all work offline.

Note: a todo item may be huge, with lots of information in many lines. Can thousands of cookies be used?

Appreciated if the text of the todo items can be read with a text editor, ideally with one todo item being stored in each file if possible.

Appreciated also if the order of todo items can be stored in the date stamps of the files, and if each file can be named after the first words of its content. The idea being that you can view the todos in order with a file manager.

Firefox does this for me. As far as scripts, as long as those are saved locally, it can all be done offline. Nearly any web browser will do this. I suspect that you'll just get a lot of answers biased by the preferences of the responder.

I think there are many obstacles because of security-driven limitations in scripting capabilities. You just can't do whatever you want with local files. Maybe DOM storage can do it? Cookies?

For the reasons you mention, the simplest solution is to basically download a calendar (browser+javascript) app with a jazzy front end and storing the todo list as a cookie and VOILA ..

Next read the script carefully, understand the structure of the cookie data and write routines (a) export the cookie data to a file and (b) import it from the file. You would need a web server for this (can reside on localhost).

OK

Are you aware of an actual calendar app that stores todo items in cookies?

Note I have over a thousand todo items to store, a single cookie is not big enough at 4 kB.

YES

There used to be a site called as javascriptkit.com or javascripcode.com or something that had a lot of downloadable examples and entire routines and html code. I definitely saw one on this. I will download it over the weekend, check and get back.

Obviously cookies are no substitute for a database and it are not portable

OK