The idea is to have a button in each page. On click, this button would pop-up a model with the same "Add Link" form from the extension. The user will be able to add a link from that form straight into the extension.
Choose a user (somehow), and with a click a new tab would open with the selected user's links. Also would be cool to be able to filter which group the selected user posted in (but the user who selected has to be in the selected group to view the links there). The dropdown menu to choose which group the selected user has posted in could have the same location as the dropdown menu to choose the group in the main "Wall" tab.
A like button on each post that will show how many likes this post got and who liked it.
extra: when clicking the button it should notify the poster of who liked the post. (this could be configurable to be turned off.
Upon trying to click the comments/like/etc... the icon is so small that the user ends up clicking somewhere else, which leads to the link opening and the extension to be unfocused (closed).
Consider making the icons bigger, or having a wrapper around them so that a miss-click does not lead to that result.
Included an image to show which icons I mean specifically. I have no image editor but they are clear (the ones under the link title)
Comments on each post that would work like replies in Slack. An indicator of the number of comments will be on each post and clicking on the comments would expand the list of comments with an input box to add a new one
As explained by the owner of the extension before, signup with email verification, and OAuth from famous social media platforms that would allow for easier, more reliable authentication.