Siddur Mesorat Moshe is a siddur whose text follows the rulings of the Rambam. I received a copy a couple of weeks ago and am now using it daily. A completely never-seen-before thing is that there's no Aleinu leshabeach in any of the t'fillot in this siddur.
I thought it was an essential prayer as it's attributed to Yehoshua. Is it only a late additional element to the t'fillot? Wasn't it in common use in Rambam's era or did he opt it out? Was the prayer adopted officially & universally only after Rambam's time?