My understanding is that the LXX is often a rather poor translation. The most famous error is of course confusing “young woman” with “virgin” but there are many others. Other times the translators were engaging in something closer to paraphrase than translation. And sometimes they were apparently translating a quite different text from the Hebrew one that is preserved today. (The book of Jeremiah being one example.)

The LXX is by no means worthless as a text-critical witness and there are many instances where it makes more sense than the masoretic text. But in most cases it is the other way around.

I thought Judaism did not use textual criticism for their Bibles*? Surely the Hebrew text that is read in synagogues is the Masoretic text, for example? I know the JPS claims to translate the Masoretic text exclusively in its Tanakh translation, though in practice it uses text-critical emendations in a few places.

Among Protestants the interesting thing is that even many fundamentalists that believe in young earth-creationism are willing to accept textual criticism of both the New and the Old Testament.

*That Reform and Conservative Judaism accepts scholarly inquiry into the origins of the masoretic text is something quite different. Just like they may accept the documentary hypothesis for the origin of the Torah but still view the final redaction as the inspired version they may view the masoretic text as inspired while accepting that it contains scribal errors.

Also Jews have also been willing to accept textual criticism in recent times. It’s almost entirely Reform and Conservative Jews (and left wing Orthodox) but then again the right-wing Orthodox might be considered as equivalent to those fundamentalist Christians that wouldn’t touch criticism with a 10 foot pole.

The Catholic church hasn’t used the LXX in a long time for the stories in the Hebrew Bible. Modern Catholic Bibles are translated from the Masoretic Text, with text-critical emendations. Before that they used the Vulgate, the latin bible, and translations of it. The Vulgate OT was originally translated mainly from Hebrew manuscripts, predecessors of the Masoretic Text.

The catholics however have a number of books in their Old Testament that were either written in Greek or where the Hebrew Vorlage is lost. Theses are translated from the LXX.

The protestants have also never regarded the Masoretic Text with the same reverence as the Jews. In modern times they are often quite willing to embrace textual criticism, even the more fundamentalist ones.