ExtJS3 is now outdated and replaced by ExtJS4. Sencha has provided a compatibility pack and a migration guide:
http://www.sencha.com/blog/ext-js-3-to-4-migration/
There's a list of new items in version 4:
http://www.sencha.com/products/extjs/whats-new-in-ext-js-4/
but I don't see anything particularly compelling; the main motivation would be to attempt to keep in line with browser compatibility and to improve startup time. There are also some theme improvements.
While we're at it, there are a number of places in the code that things could be cleaned up. None of them are critical, but cleaning up function names, splitting some things into multiple functions and so on could be worthwhile.