Page jitter when a scroll bar exists in Firefox

In Firefox, the default page does not exceed one page. If no scroll bar is added to the page, some elements will temporarily change the page height. For example, if tooltip is used, a prompt tool like this will cause page jitter when the scroll bar appears.
The solution is to add CSS:

Body {overflow:-moz-scrollbars-vertical ;}

Enough ^_^

In fact, the above question is not very important, A serious case is that partial jitter occurs when some part of the page uses a scroll bar and uses tooltip on the page (for example) this is a very serious problem. I accidentally found that the above method can be used to solve it.