The fix works for navigating
Bug 1791322 Comment 20 Edit History
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The fix works to block downloads without the proper attribute on navigation and on user click. It is included in the WIP. The WPT tests however are not working properly as it's still saying a download was completed. I find it strange that the GeckoView Test Runner page doesn't actually show the download button, and it also makes it difficult for me to debug outside of the automated test. Will be working on that this week.