1. Open the browser console and go to the Debugger/Sources tab.
2. Select the ./src/app.lua file.
3. Place a breakpoint on line 2.
4. Refresh.
5. Use step over to step through the code.

Observe that in Firefox each step progresses to the next observable statement, as you might expect. However, in Chrome, when you step through the code, the highlight stays on line 4 for five clicks of the step over button each time.

I believe this may be due to the fact that that single line of Lua code is translated to a number of lines in JavaScript. The Chrome debugger appears to be stepping through the generated code statement by statement, rather than the code that is visible in the debugger. As a developer, the Firefox method is preferable/more appropriate.

Source