I found out that if the equation button is removed from the Atto toolbar, some buttons such as the HTML button stop working and produce JS errors.
This happens only in the settings pages.
To recreate this issue:
- Go to Site administration -> Plugins -> Text editors -> Atto HTML editor -> Atto toolbar settings.
- Remove the equation from the Toolbar config field and save.
- Go to Site administration -> Front page -> Front page settings.
- Enter some text.
The HTML button fails to work and the Paragraph menu can be opened but cannot be closed.
Further checking revealed that the equation button requires the "tabview" component which appears to be essential for the editor to work correctly.
I'm working on 2.7 so I selected the lowest version available (2.7.6).
Since I can't install and run 2.9 on my system I only checked it on 2.7 so I don't know if this issue was fixed in 2.8 or 2.9.
In case this happens on these versions I think the best solution would be to add the requirement in the editor's core, instead of relying on a plugin that can be removed anytime.