The reason Feedbro doesn't render feed XML URL automatically as HTML when you open such link in a normal tab is that it would require Feedbro to scan ALL URLs that are loaded by the browser (and check if it looks like a feed based on HTTP headers and/or content). This would needlessly slow down the browser a lot.

Since that is a VERY marginal use case and with Feedbro you can use "Find Feeds in Current Tab" and see the link rendered as HTML when needed, such automatic conversion was not and will not be implemented.

Also the whole point of a feed reader is that you don't have to open feed links in normal tabs all the time. Feedbro will aggregate the articles from multiple sources and then you read those using the Feedbro UI.