Icons do not show for certain file types, as a result file can not be (clicked) opened with default application.
For example .h and .txt file show a clickable icon, when clicked the configured default app opens the file. This doesn't work however for .c and .js files. Helper configuration has xdg-open configured, all files open correctly when using xdg-open on the command line. An attempt to fix this issue, was made in commit https://git.enlightenment.org/apps/terminology.git/commit/?id=b2fe5145d90a1a36c7d7168d3dd8c7887b56512e