Hi,
I confirm that you can use Lightstreamer libraries with HTML5 offline application caching.
I was able to successfully run an offline application on Firefox 3.6, Chrome, Opera 11 and Safari 5
I still have not tried mobile browsers (Android Browser, iOs Safari, Opera Mini and Mobile should all support this feature, see http://caniuse.com/#feat=offline-apps ).

All you have to do to let the application work is specify lightstreamer files in the manifest file like this:

Code:
lscommons.js
lspushpage.js
lsengine.html?build=XXXX
lsengine.js?XXXX
lsblank.html?domain=yourdomain.com
lsform.html?yourdomain.com
where yourdomain.com is the actual domain you're using in your setDomain calls and XXXX is the build number of the lightstreamer libraries (you can find it in the library folder inside the build.number file. If you prefer you can also find it as last piece of the Lightstreamer.version property available on the page once the libraries are included)

Please also note that only Chrome seems to properly support absolute file paths; To let the app work I had to place lightstreamer libraries in a folder that is a son of the folder where the "main" html file is (though I did not try relative "../" paths).

let me know if you have any issue,
HTH