When I try add this to my debug build mozconfig... ac_add_options --disable-webspeech ...my build fails, with this output: { /mozilla/dom/ipc/PContent.ipdl:20: error: can't locate include file `PSpeechSynthesis.ipdl' Traceback (most recent call last): File "/mozilla/config/pythonpath.py", line 56, in <module> main(sys.argv[1:]) File "/mozilla/config/pythonpath.py", line 48, in main execfile(script, frozenglobals) File "/mozilla/ipc/ipdl/ipdl.py", line 127, in <module> if not ipdl.typecheck(ast): File "/mozilla/ipc/ipdl/ipdl/__init__.py", line 35, in typecheck return TypeCheck().check(ast, errout) File "/mozilla/ipc/ipdl/ipdl/type.py", line 596, in check if not runpass(GatherDecls(builtinUsing, self.errors)): File "/mozilla/ipc/ipdl/ipdl/type.py", line 586, in runpass tu.accept(tcheckpass) File "/mozilla/ipc/ipdl/ipdl/ast.py", line 135, in accept return visit(self) File "/mozilla/ipc/ipdl/ipdl/type.py", line 694, in visitTranslationUnit pinc.accept(self) File "/mozilla/ipc/ipdl/ipdl/ast.py", line 135, in accept return visit(self) File "/mozilla/ipc/ipdl/ipdl/type.py", line 758, in visitInclude inc.tu.accept(self) File "/mozilla/ipc/ipdl/ipdl/ast.py", line 135, in accept return visit(self) File "/mozilla/ipc/ipdl/ipdl/type.py", line 711, in visitTranslationUnit if inc.tu.filetype == 'header': } (This is a clobber build.)

Looks like this happened in the transition to moz.build. Unless you beat me to it, I'll have a patch ready soon.

Thanks!