Prior to this viewing, "Firewalker" was one of only five X-Files episodes I had only seen once. I figured there was no need to watch it again, because I found it neither bad nor good, and just boring. Imagine my surprise as I re-watched "Firewalker" and found it very entertaining, and actually a very good episode in every way.
If you've read any of my comments on "The X-Files" episodes you would know that I am not a fan of Howard Gordon (who would go on to become the boss at "24", a show I'm really not a fan of), especially with his former writing partner Alex Gansa, not that I like him much on his own either. I find his scripts to be generally flat and uninspired, and the dialogue to be fairly poor, which is something you can usually expect great things from when it comes to "The X-Files". With "Firewalker" I think he's done extremely well, in spite of the inconsistencies others have pointed out. I still prefer "Ice" (which certainly is very similar to this) because it's got an absolutely classic script with memorable dialogue, but "Firewalker" is still a fine episode.
"Firewalker" actually has a much stronger atmosphere (thanks to the creepy and mysterious volcano setting) and group of guest characters than "Ice" does. Another IMDb user noticed that you could read Trepko and Jesse's characters as parallels to Mulder and Scully, which is not only a sound observation, but something I can't believe I didn't pick up on. David Nutter (who also directed "Ice") returns and does a great job of creating genuinely claustrophobic atmosphere. The guest cast is outstanding as well.
"Firewalker" is not a great episode, but it's very good, almost surprisingly so, and deserves more credit than it gets.
8/10