(In reply to Tom Schuster [:evilpie] from comment #0) > On Windows at least we don't actually use the extraMimeEntries to enhance the information returned by `nsExternalHelperAppService::GetFromTypeAndExtension`. We do, but too late (namely in the platform-specific code), and can end up with nonsensical extensions provided by the server instead. This is specifically about the code at https://searchfox.org/mozilla-central/rev/b2433a832c250c55255e0ee37d05192d04f20427/uriloader/exthandler/win/nsOSHelperAppService.cpp#450-454 which attempts to get a file extension that fits the mimetype. This code does not use the builtin mimetype-to-extension mappings, relying only on the registry.
Bug 1690539 Comment 1 Edit History
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(In reply to Tom Schuster [:evilpie] from comment #0) > On Windows at least we don't actually use the extraMimeEntries to enhance the information returned by `nsExternalHelperAppService::GetFromTypeAndExtension`. We do, but too late (namely in the platform-agnostic code), and can end up with nonsensical extensions provided by the server instead. This is specifically about the code at https://searchfox.org/mozilla-central/rev/b2433a832c250c55255e0ee37d05192d04f20427/uriloader/exthandler/win/nsOSHelperAppService.cpp#450-454 which attempts to get a file extension that fits the mimetype. This code does not use the builtin mimetype-to-extension mappings, relying only on the registry.