Tosefta for Chullin 220:5

Rabbi Yosei says, we may pickle terumah onions in chullin vinegar, *but we may not pickle terumah onions in terumah vinegar (*MS Erfurt omits "but...vinegar"), and it goes without saying that chullin onions in terumah vinegar [is forbidden]. Rabbi Akiva says, all [foods] cooked together are permitted with meat (but see Ter. 10:11, "except with meat"). [Terumah] meat [cooked] with [chullin] meat is forbidden, and all [foods] that are [both] cooked and mixed together (following MS Erfurt), behold, they are forbidden. Rabbi Eliezer says, liver renders [other foods] forbidden, and *is rendered forbidden [by other foods]. [*Note: per MS Erfurt, "is not rendered forbidden," see also Ter. 10:11.] Rabbi Yishmael son of Rabbi Yochanan ben Berokah says, stewed [liver] renders [other foods] forbidden and is not rendered forbidden [by other foods]. Boiled [liver] renders [other foods] forbidden and is rendered forbidden [by other foods].