I have used many kinds of wood, including pine. In general, soft woods rot and grow the slime coat faster than other types. I typically have plecos in my tanks and they readily clean the wood and keep decay in check. Think of soft woods more as temporary decor. I have used soft wood driftwood for around a year or so before discarding the piece and rescaping the tank. As long as weekly water changes are performed, wood generally will not influence your water quality in a significant way. Regardless of the wood you use, it should be a solid piece that is not soft or otherwise already begining to decompose.
I would never suggest trying a new variable with super sensitive species, and I have never used fir. I have never had wood cause a problem with my fish health and I have used multiple species of pine. Water changes help remove tannins and any other chemicals. Properly boiling and/or soaking the wood prior to using in a tank will greatly improve the quality of the wood and decrease the chemical load in the wood itself
the guy says it is from a fir tree, I pretty much assume bad since fir is pine, he said it was a pitch? in the middle of tree and will not rot, but as stated above isnt pine bad for aquariums
