Is borosilicate glass toxic?

Borosilicate glass has a melting point of 1648 C, so nothing will happen to its composition when heated to a mere 210 C.

Borosilicate glass is not toxic, it is used heavily in both cooking ware and in laboratory glass ware. Heating it in the way you describe will not cause any bad by-products. On the other hand, tobacco smoke is quite toxic.