Makes a W3C alwaysMatch capabilities object.

    Filters out capability names that are not in the W3C spec. Spec-compliant
    drivers will reject requests containing unknown capability names.

    Moves the Firefox profile, if present, from the old location to the new Firefox
    options object.

    :Args:
     - caps - A dictionary of capabilities requested by the caller.

def _make_w3c_caps(caps):
    """Makes a W3C alwaysMatch capabilities object.

    Filters out capability names that are not in the W3C spec. Spec-compliant
    drivers will reject requests containing unknown capability names.

    Moves the Firefox profile, if present, from the old location to the new Firefox
    options object.

    :Args:
     - caps - A dictionary of capabilities requested by the caller.
    """
    caps = copy.deepcopy(caps)
    profile = caps.get('firefox_profile')
    always_match = {}
    if caps.get('proxy') and caps['proxy'].get('proxyType'):
        caps['proxy']['proxyType'] = caps['proxy']['proxyType'].lower()
    for k, v in caps.items():
        if v and k in _OSS_W3C_CONVERSION:
            always_match[_OSS_W3C_CONVERSION[k]] = v.lower() if k == 'platform' else v
        if k in _W3C_CAPABILITY_NAMES or ':' in k:
            always_match[k] = v
    if profile:
        moz_opts = always_match.get('moz:firefoxOptions', {})
        # If it's already present, assume the caller did that intentionally.
        if 'profile' not in moz_opts:
            # Don't mutate the original capabilities.
            new_opts = copy.deepcopy(moz_opts)
            new_opts['profile'] = profile
            always_match['moz:firefoxOptions'] = new_opts
    return {"firstMatch": [{}], "alwaysMatch": always_match}