Since origin servers do not always provide explicit expiration times,
a cache MAY assign a heuristic expiration time when an explicit time
is not specified, employing algorithms that use other header field
values (such as the Last-Modified time) to estimate a plausible
expiration time. This specification does not provide specific
algorithms, but does impose worst-case constraints on their results.
The standard does not say what heuristics should be used, so Firefox’s heuristics is no more “legitimate” than Chorme/Safari’s heuristics of expiring immediately when Content-Dispostion is present.
“Firefox legitimately treats...” is highly misleading, making it sound like Firefox is more standard-compliant, but it’s not; it’s just different.
I am fairly confident that the article is not trying to imply that Chrome/Safari are NOT standards compliant. The author seems to be trying to heavily emphasize that this is not a Firefox bug, and that Firefox can legitimately do this while being standards compliant.
I feel like the author was anticipating a lot of people blaming Firefox for this incident, and is attempting to shut those responses before they get made.
I think that trying to write to the responses you expect from your audience unfortunately ends up with these kinds of miscommunications of intention more often than not.
And it's allowed to treat it differently than the other browsers. That's what "legitimately" means. And that needs to be pointed out, because Twitter was very careful to avoid saying it wasn't a Firefox bug.
I'm not. If copied without formatting as code blocks, the text would be a lot more readable and wouldn't require horizontal scrolling on narrow viewports.
“Firefox legitimately treats...” is highly misleading, making it sound like Firefox is more standard-compliant, but it’s not; it’s just different.