bug 1768060 patch adds support for lexical variables, so, if we can go with it, converting `var` or `this.foo = ` with lexical won't break not-in-tree code
Bug 1766761 Comment 7 Edit History
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bug 1768060 patch adds support for lexical variables in `Cu.import` return value, so, if we can go with it, converting `var` or `this.foo = ...` with lexical won't break not-in-tree code