Can't build www/firefox on 8.3

[Mikhail T.]

Running:

    % make CC=gcc46 CXX=g++46
    ....
    /mi/ports/www/firefox/work/mozilla-release/content/base/src/nsContentUtils.cpp:
    In static member function 'static bool
    nsContentUtils::GetSVGGlyphExtents(nsContentUtils::Element*, const
    gfxMatrix&, gfxRect*)':
    /mi/ports/www/firefox/work/mozilla-release/content/base/src/nsContentUtils.cpp:6987:38:
    error: ambiguous overload for 'operator=' in '* aResult =
    displayFrame->nsISVGChildFrame::GetBBoxContribution((* & aSVGToAppSpace), 31u)'
    /mi/ports/www/firefox/work/mozilla-release/content/base/src/nsContentUtils.cpp:6987:38:
    note: candidates are:
    ../../../dist/include/gfxRect.h:59:19: note: gfxRect&
    gfxRect::operator=(const gfxRect&)
    ../../../dist/include/gfxRect.h:59:19: note: gfxRect&
    gfxRect::operator=(gfxRect&&)
    gmake[5]: *** [nsContentUtils.o] ??????? 1
    ...

Any ideas? Thanks! Yours,

    -mi