Version: v. 184.108.40.206 (Qt - 4.8.7)
- Create a new session with type Single application and set Command to "Firefox" (with first F in uppercase). Click OK to save it.
- Choose "Session preferences" to edit the session.
- Set Command to "firefox" (all letters in lowercase).
- Either click OK to save it or just click to focus on some other field.
- The Command changes back to "Firefox" (with first F in uppercase).
There seems no way to correct such misspell. I had to delete and create a new session.