Why is Dijkstra's Algorithm more popular compared to Grassfire algorithm?
In grassfire the distances are constant. All of your neighbors have equal length. In a weighted graph, grassfire will fail. 

Graphfire is actually based on a small modification of BFS.

The Dijsktra works on weighted graphs, too.

Note: If all costs are equal, Dijkstra = BFS

Know the difference, and use them according to your need.