browsers = Browser.objects.all()

    app = Application.objects.get_or_create(name=app_name)[0]

#первый вариант:
    supported_browsers = []
    not_supported_browsers = []

    for b in browsers:
        if b in app.browsers.all():
            supported_browsers.append(b.__unicode__())
        else:
            not_supported_browsers.append(b.__unicode__())

#второй вариант:
    supported_browsers = [ b.__unicode__() for b in browsers if b in app.browsers.all() ]
    not_supported_browsers = [ b.__unicode__() for b in browsers if b not in app.browsers.all() ]