I am migrating from Waterfox and this is a feature I miss a lot.
Basically what it says in the title. Add an option to display a pop-up whenever clicking on an “app link”, which asks the user whether they want to leave the browser.
This adds extra security, preventing leaving the browser on accident or due to a series of redirects, as well as gives the user more control in some cases. Personally, I frequently encounter cases where certain links don’t open correctly in apps and need to be opened in the browser, which forces me to go dig through settings and temporarily disable link opening for that app.