As of now, this would ship 2020-06-02 and Chrome's removal possibly 2020-06-22 or a month later. Shipping this with ESR 78 would mean to support it another full year. (I assume deprecations do not happen within an ESR release.) It doesn't even take an hour to change AppCache into a simple ServiceWorker and to learn the basics around it. https://thomashunter.name/posts/2019-04-30-service-workers > The Application Cache came with a few footguns. For example, if the cache file is accessed and has been altered, this would signify that the site has been updated and the browser should rebuild the cache. However, if the filename for the cache was added to the cache file, the cache would cache the manifest and the user would never download newer updates. See [Application Cache is a Doucebag](https://alistapart.com/article/application-cache-is-a-douchebag/) for more footguns.
Bug 1619673 Comment 10 Edit History
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As of now, this would ship 2020-06-02 and Chrome's removal possibly 2020-06-23 or a month later. Shipping this with ESR 78 would mean to support it another full year. (I assume deprecations do not happen within an ESR release.) It doesn't even take an hour to change AppCache into a simple ServiceWorker and to learn the basics around it. https://thomashunter.name/posts/2019-04-30-service-workers > The Application Cache came with a few footguns. For example, if the cache file is accessed and has been altered, this would signify that the site has been updated and the browser should rebuild the cache. However, if the filename for the cache was added to the cache file, the cache would cache the manifest and the user would never download newer updates. See [Application Cache is a Doucebag](https://alistapart.com/article/application-cache-is-a-douchebag/) for more footguns.