In the case of the firs it refers to the sap, but for a bottle like this I think it was something similar to bitters: https://en.wikipedia.org/wiki/Balsam_(drink)Yep. Smooth bases. The HARRISONs ICELAND BALSAM has a lovely pot stone in the blank side.
What the heck was medicinal Balsam? When I think of balsam, I think of Fir trees.