Q. Re- question above. Often the glass cups use for Chanuka lights, are rounded on the bottom and can’t stand by themselves. Is that a problem?
A. Chesed L’Avraham (quoted in Shaarei Teshuva (673: 13) rules that one may not light Chanuka candles using the shells of (fruit of) trees or onions, as a keli or utensil is required, He adds that any utensil that cannot stand by itself, without additional support should not be used. Avnei Nezer (500) mentions that some Rishonim support his position. Therefore, following their opinion, one may not use a candle just attached (by melting the base) to a counter or to the ledge of a window. (See Shevet Halevi 8: 157).
Nitei Gavriel (21: 5) and Piskei Teshuvos (ibid. n. 43) suggest that following that opinion a rounded glass cup that cannot stand by itself may not be used as it may not qualify as a keli. However, Mishna Berura (611: 18) mentions that one mat attach candles to a wall.
Nitei Gavriel and Piskei Teshuvos also mention that other Poskim don’t mention at all that a keli is essential for lighting Chanuka lights. (See Oz Nidberu 13: 49, Shvus Yaakov 1: 33).
Horav Shlomo Miller’s Shlit’a opinion is similar and one may use, as many do, a glass cup even if it cannot stand without the support of the menorah. In regards to the prior question on using glass cups in a silver menorah, the Rov added, that when they cannot stand by themselves, they certainly become annulled to the menorah itself and are essentially part of it.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a