When I moved my mouse cursor over Impact (Approximate no. of people reached) in my [Pro Webmasters Profile Page][1], few of the contents are not visible. They are going behind the header banner. But I checked 
some SE sites and they are looking fine. I checked through Firefox 40.0.3. Does it is a bug? Do SE site is not compatible with latest Firefox version?

*Screenshot:*

**Pro Webmasters:**

>[![enter image description here][2]][2]

**Meta SE:**

>[![enter image description here][3]][3]

This other bug report on User Experience site proves it's not specific only to one site: https://ux.meta.stackexchange.com/questions/1966/people-reached-tooltip-covered-by-navigation-header


  [1]: http://webmasters.stackexchange.com/users/current
  [2]: https://i.sstatic.net/es8A4.png
  [3]: https://i.sstatic.net/sp5X7.png