The guidelines for this extension literally say that a slur targeted at trans people is "not enough" to mark as anti-trans.
The developers have as of recently been exploiting this extension's purpose to mark subsets of the trans community they personally don't like by flagging them as anti-trans while a lot of pro-trans tagged accounts can say highly bigoted things about other groups of trans people such as trans men and non-binary people.
This is no longer an actual add-on to help trans people online but a way for transphobes to pretend they are trans-friendly while harassing trans people

edit: this developer reply is not only using rhethoric to attack non-binary people baselessly by mentioning "binary trans woman" is used against women who transition (usually transphobes wouldn't be in favor of non-binary people either so i dont understand why the claim of "long been used" was even attempted) but also avoiding the clear slur criticism by saying "controversial terms" instead
As a trans woman these kind of attempts to come up with false reasons to muster community in-fighting by falsely tagging non-binary and trans masc people as transphobic while allowing the use of slurs against those identities (like "theyfab") does nothing but make me feel unsafe about the extension if it is being misused in this way to slander and enable harassment of my fellow members of the community