How long does chrome & firefox cache a file if no "expires" or "max-age" tag is set?

Question

I would like to know what the default max-age is of an image or css file, but can't seem to find it anywhere.

Someone suggested it was only 300 seconds, but that doesn't seem to be correct.

Answer 1

The default is infinite.

As newer files are added to the cache, old ones are purged to make space. The file won't actually stay in the cache for ever.

The purge will cause the file to be reloaded if it is called for again.

Answer 2

The files will be in the cache. But they might not be used.

The rules for that is probably more complex, depending on browser, and will probably change over time. Other answeres here and here.