Steps to reproduce:
- Go to the bottom of this page: https://en.wikipedia.beta.wmflabs.org/wiki/User_talk:RYasmeen_(WMF).
- Click on Reply links starting from the comment "10th comment" and onwards.
Notice that the options under Visual mode start getting overlapping with the options "Source" and "Visual" more and more as you go towards the end of the page. At some point, all of them become completely unusable.
Screensize: Mac 13 inch.
Here are some screenshots:
Starts overlapping like this: