according to Read/WriteWeb, Firefox 3 will offer support for running web-applications offline. though it’s not yet clear on which level this might happen, this is major news for providers of service-based web-software. the biggest advantage of online-apps – using them on any device with net-access with no need to sync data – is at the same time their worst caveat – when connectivity goes down, so do online-apps and all data stored within them (that’s why it is a good idea even for fulltime Gmail-users to backup their mail via POP3).
of course, Firefox isn’t alone in trying to move web-apps offline – Adobe’s Apollo framework promotes offline-services on top of their successful Flash-platform. Flash has bee used to store data in a local cache for quite a time, as it has been the only cross-browser solution besides storing (mini-chunks of) data within cookies (Niall Kennedy gives a good overview on various methods of storing data locally). applications like Scrybe (private beta) let us anticipate the way future online/offline-apps might look&feel.
naturally, existing web-apps require heavy modification to work with any of the mentioned offline-approaches, meaning we still have to wait for real-life apps leveraging the benefits of going offline.