Lofesa edited a comment on issue #1857: firefox 65 png and gif files do not convert to webp, though jpg does. URL: https://github.com/apache/incubator-pagespeed-mod/issues/1857#issuecomment-570812465 I´m testing Firefox nightly (73) and get some png (don´t use gif) not converted and others png converted to webp. My theory about that is that the issue is related to the alpha channel. I have found in the file: `pagespeed/kernel/image/image_converter.cc` this [line ](https://github.com/apache/incubator-pagespeed-mod/blob/b4bf44cc56d8bbf17494c540dfb6ef20dfcf5073/pagespeed/kernel/image/image_converter.cc#L346) so if the alpha channel is 0, the image is not converted. In other hand, in the file `pagespeed/kernel/http/user_agent_matcher.cc` there are a [whitelist](https://github.com/apache/incubator-pagespeed-mod/blob/b4bf44cc56d8bbf17494c540dfb6ef20dfcf5073/pagespeed/kernel/http/user_agent_matcher.cc#L157) for UA with support for webp alpha. So maybe including some like `"*Firefox/7*"` to the white list may do the trick. EDIT: adding `"*Firefox/7*"` to the whitelist works. Maybe we need to add Firefox 66,67,68,69,70,71,72 to the [LegacyWebpWhitelist](https://github.com/apache/incubator-pagespeed-mod/blob/b4bf44cc56d8bbf17494c540dfb6ef20dfcf5073/pagespeed/kernel/http/user_agent_matcher.cc#L134) cause these browser support webp but don´t send `accept: image/webp` in headers. **I have no tried with gif** EDIT 2: adding firefox versions to the LegacyWebpWhitelist don´t work, maybe sending accept: image/webp is needed. Ping @oschaaf
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