Firefox crashes with 'SyntaxError: missing = in const declaration'

[Lloyd Brookes]

not sure where this line is defined (maybe a sub-module?):

for (const propName of ["availableDocumentFeatures", "defaultDocumentFeatures", "applyDocumentFeatures"]) {

but it is crashing Firefox (stable and DeveloperEdition) with this error:

SyntaxError: missing = in const declaration

i'm using the latest zuul with node v6, the brfs transform and tape.

[Lloyd Brookes]

i'll close this until i can prove it is zuul's "fault".