This bug occurs when creating a macro while using Firefox Quantum (v. 57.0).
This are the steps to reproduce the habbit:
situation: i'm in edit mode and editing a confluence page
1. create a macro (+ -> macro)
2. insert content into your macro, i.e choose from a dropdown menu or write some text in the shown modal.
3. try to save and press Return (Enter).
4. Not everytime, but it occurs that the input won't be saved and the modal exits without saving. Cursor jumps to the top of the page.
Neither Chrome or Internet Explorer (latest versions) do have this issue.
Help is appreciated since this is a major problem for a good workflow.