In my experience using the HTML5 AppCache, it is great once you get it working, but extremely brittle. If there's the tiniest thing wrong with it the browser ignores the entire file and, annoyingly, rather than use the browser's ordinary cache, re-loads everything from scratch off the server.
Worse, browsers will not re-load the manifest file unless its text content changes. So you might tweak your server headers or something to fix it, but unless the content of cache.manifest.php changes the browser will blindly ignore it and do exactly what it did last time. So it could have been broken, then you fixed it, but browsers are ignoring the changes because the text content of cache.manifest.php hasn't changed. This even seems to be immune to clearing your browser cache, which is part of what makes it so confusing - app cache is really, really serious about caching.
To get around this, text changes in comments count, so have a comment at the top with a version or timestamp or the date (e.g. # Version 1.2) and change that when you want the browser to "notice".
Then, the browser still won't immediately use it! The way the app cache works is the next time you load the page it will do exactly what it did last time yet again, and start checking for an update in the background. So you probably want the console up, wait for something like "updating..." then "complete", then hit Refresh and the browser will finally start using the new version. At last!
All in all it can be a right pain to get working. However, once it's working it's almost bulletproof: you can pretty much rest assured anything listed in the cache manifest is only every downloaded once, ever, for all time, per user, until you change the text content of the file.
Browser standards compliance is pretty good these days, so my best guess is you actually have it working, but you checked Chrome last and it's the only browser which has cached the manifest file correctly. During development you might have had it broken, but Firefox and Opera are clutching their old manifest files to the death. I bet you also tried clearing the browser cache in Firefox and Opera, which probably did nothing - you need to change the text content of the file and double-refresh before either Firefox and Opera will finally give up their broken versions of the manifest file and start using the one which works which you probably uploaded ages ago.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
