Firefox and Expires headers

[mattmachell]

Discovered this fun appcache fact on some recent work. With Firefox if your cache manifest has an HTTP Expires header set to a past time, then the manifest will not download.

This can be a problem if your framework adds these automatically to get round overly aggressive proxies.

[jokeyrhyme]

Looks like IE11 does this too. All files in AppCache manifest listing must have HTTP headers that suggest caching.