When downloading a file, we check for existing mime types and construct a new one if it's unrecognized. Mime types have a flag, alwaysAskBeforeHandling, that determines whether the unknown content type dialog should be opened before handling the file. Before bug 1733492, the default value for that flag was simply true. Since the new downloads flow is intended to avoid unnecessary steps, the default value was changed to the inverted value of the new downloads panel improvements pref. This patch adds a new pref that the mime info constructor will read in configuring the flag's value. If the improvements pref is not enabled, then the flag will be true, so the UCT dialog will open. If the improvements pref is enabled, then it'll use the value of the new pref. Also add a an interface for the pref to the about:preferences UI. This interface is disabled when the improvements pref is disabled, because the pref doesn't really do anything in that case. But that shouldn't matter much since that pref is enabled by default now. I'm updating some tangentially related test files since they happen to be touched slightly by this change. Strictly speaking they would still work, but if the pref value was somehow changed from the default they would fail.
Bug 1747343 Comment 19 Edit History
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When downloading a file, we check for existing mime types and construct a new one if it's unrecognized. Mime types have a flag, alwaysAskBeforeHandling, that determines whether the unknown content type dialog should be opened before handling the file. Before bug 1733492, the default value for that flag was simply true. Since the new downloads flow is intended to avoid unnecessary steps, the default value was changed to the inverted value of the new downloads panel improvements pref. This patch adds a new pref that the mime info constructor will read in configuring the flag's value. If the improvements pref is not enabled, then the flag will be true, so the UCT dialog will open. If the improvements pref is enabled, then it'll use the value of the new pref. Also add a an interface for the pref to the about:preferences UI. This interface is disabled when the improvements pref is disabled, because the pref doesn't really do anything in that case. But that shouldn't matter much since that pref is enabled by default now. I'm updating some tangentially related test files since they happen to be touched slightly by this change. Strictly speaking they would still work, but if the pref value was somehow changed from the default they would fail.