A synonym for opposing something firmly is to "resist" it.
The word "firmly", meaning "in a firm manner", is an adverb.
the quality or fact of being able to grip something firmly; grip.
In a firm manner.
it means if you ask something obvious you will get a wrong answer as it is obvious.
the quality or fact of being able to grip something firmly; grip.
As an adjective:Being firmly settled in habit; inveterate; chronic.Having been ratified; verified; unchangeableHaving received the rite of confirmation.
to firmly secure something
Stable.
If it's a meaning you want, 'sternly' means 'harshly' or 'firmly'.
sturdy, dense, forcefull
Yes, it is an adverb. It is the adverb form of the adjective firm, and means in a firm way, or in a determined manner. E.g. The lines were firmly attached to the boat. The governor firmly refused to compromise.