Placing ScriptSafe in the "More tools..." menu in Firefox breaks layout

[tim-elmer]

When the icon for ScriptSafe is placed in Firefox's "More tools..." menu, the add-on layout breaks, cutting off the right side of the menu:

Works as expected when placed in the toolbar outside the "More tools..." menu... Perhaps the "More tools..." menu imposes a maximum width?

Affected: Firefox 57.0.2 on Windows 10 Pro v1709, build 16299.98