(Note: this issue is probably the same issue as reported in 1439701 - Mouseover link tooltip url persistent through click and page load. While that user marked that issu… (funda kabanzi)
(Note: this issue is probably the same issue as reported in 1439701 - Mouseover link tooltip url persistent through click and page load. While that user marked that issue as solved, their "resolution" makes fairly clear that the issue was never really solved.)
When hovering over a link, Firefox will typically show a tooltip at the bottom left with the link's address. Typically, this tooltip disappears when the mouse is no longer hovering over the link (whether because you moved the mouse or clicked the link). However, in some circumstances, the tooltip doesn't disappear when it should. Here's an example of how to reproduce the issue:
1. Go to YouTube
2. Search for anything.
3. Choose a result, and click on the thumbnail. (NOT on the title.)
Expected result: the tooltip showing the URL of the video disappears since the video is loading and the link you clicked no longer exists on the page.
Actual result: the tooltip persists. Once you hover over any other link on the page, behavior will return to normal.