how can I identify an element which disappears after any action?

Here https://www.linuxquestions.org/questions/linux-newbie-8/ hovering a mouse over any post brings up a window with its text. How can I block it? Or rather how can I identify what to block? It closes on right-click so I cannot use ublock's 'block element'. F8 from dev tools' debugger doesn't work either - slightly different behaviour in firefox and chromium, but no effect in either. Is there a relatively easy way?

Please note that I am looking not for a rule for this particular site but for generic approach to identifying annoyances of this kind.