no, I didn’t test the default settings because I was satisfied with the speed tests. However, I managed to work around the issue by creating popups directly within the editor (and not via Elementor’s “modal window” tool), and by disabling them on Mozilla.
Since I had been looking for a solution for a while without success (I tried a looooot of settings, contacted Elementor support, my hosting provider, etc.), I finally disabled the Mozilla popup, so the issue is no longer visible. However, here is a screenshot of what was happening on mozilla.