Works as designed.

1. When you shift-A a feed or folder with "show only unread" mode active, there's really no point in removing articles from the screen. Leaving them visible lets the user to undo the operation fully or partially.

2. When the user moves to the next feed or folder with shift-N, it's not guaranteed that the user wants to load the contents (especially if the user has automatic "mark as read" mode on). The user might very well want to skip to the next one without loading the contents. Therefore you need to press shift-O to load the contents. So shift-N, shift-O combination is the magic.

You can reach us via the Support email address that is on the front page of the Feedbro app page here in AMO. Reviews aren't meant for support requests or bug reports.

That feed is incorrectly embedding YouTube videos. In the feed content they use tags like:
[iframe width="320" height="320" frameborder="0" src="https://www.youtube.com/watch?v=pi846_OMVRA">[/iframe>

which embeds the entire YouTube video page (including comments etc) and makes the browser to autoplay the video.

Instead, they should be using proper embed URL which for that particular video would be:
[iframe frameborder="0" src="https://www.youtube.com/embed/pi846_OMVRA">[/iframe>

Note. html tags modified slightly (< to [) to make them visible here.

This won't be implemented. The reason is that the number on the Feedbro WebExtension icon tells the number of unread articles. The user might very well want to retain that information even after clicking the icon and reading a few articles. That's because the number would then remind the user that there are still some unread left.

If you want that number to go away, you can always use "Mark all as read" (first select the "All Items" main menu item and then click the green checkmark icon or press Shift+a) which will then mark all unread articles as read.