A side-note. That response header (304 Not Modified) shows the file is already in the browser's local cache so nothing is fetched - hence no Content-Type, etc.
During testing I have been clearing the browser cache using Edit > Preferences > Privacy
With "Ask me before clearing private data" selected press the "Clear Now..." button and deselect everything but "Cache" then press the "Clear Private Data Now" button.
Thanks Hew.
A side-note. That response header (304 Not Modified) shows the file is already in the browser's local cache so nothing is fetched - hence no Content-Type, etc.
During testing I have been clearing the browser cache using Edit > Preferences > Privacy
With "Ask me before clearing private data" selected press the "Clear Now..." button and deselect everything but "Cache" then press the "Clear Private Data Now" button.