Hello patrickfox,

You can open another tab by long pressing a link and then tap "Open link in new tab"

unfortunately this doesn' work! Firefox klar only support one single tab (window)!!!

Then i am afraid this is not yet implemented in Firefox Focus/Klar for iOS, If it is important for you to selectively close tabs while still having a private browsing environment, I would recommend you to use the standard Firefox for iOS and enable Tracking Protection, Block cookies (this can be done in Safari tap Settings > Safari > Block Cookies) and you can either clear your browsing history once in a while or permanently disable Firefox remembering your history on iOS.