Q. (Re- question 2200 above). Is this year, when Erev Yom Tov is Shabbos any different in regard to Tosefes Yom Tov on Shavuos?
A. We mentioned above that Halichos Shlomo (12: 9) and others are of the opinion that with the lighting of the Yom Tov candles, which is done when it is still day, one complies with the mitzva of Tosefes Yom Tov. Obviously, this can not be done when Erev Shavuos is Shabbos. Besides, some Poskim maintain that women should always light candles on Shavuos only at night. (Piskei Teshuvos (494: 2).
Additionally, since it is Shabbos and the melacha prohibition already is in effect, there is no point in accepting additional Tosefes.
Horav Shlomo Miller’s Shlit’a opinion is that there is still place to accept Tosefes Yom Tov on melacha prohibitions such as Muktza, which in some aspects it is more severe on Yom Tov than Shabbos.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a