When opening the HTML5Launchhelper, are you opening up a web browser and typing in: http://localhost:8000/PROJECTNAME.html? If not, this is how you’d have to set it up if you’re testing it locally.
I think the issue occurs when he tries to launch the web browser on the page directly from the UE4 editor, and his user profile name on Windows has a space in it, e.g. “Firstname Lastname”. It might also occur when he double-clicks directly on HTML5LaunchHelper.exe in the output directory, though not quite sure about that.
Looking at line 9 of the paste, this does look like missing quotes " " around the temporary profile filename that is passed to Firefox.
However searching in UE4 source tree for that piece of code, it has
in \UnrealEngine\Engine\Source\Programs\AutomationTool\HTML5 line 471, which does clearly have escaping. Perhaps some interaction with Windows shell later strips that escaping, or it’s needed in another place as well. Not quite sure…
Anyways, there some ways to avoid this for a somewhat comfortable workflow:
If you are using Firefox to develop, then you can just drag and drop the main .html page to Firefox on top of the Firefox browser window to run.
Chrome doesn’t allow XHRs to succeed if running via file://, so for that, you can launch “python -m SimpleHTTPServer” from command line in the output directory, and navigate to http://localhost:8000/ to run the page.
As stated by juj I was indeed launching directly from the editor. So there are not that many reproduction steps, it’s just clicking on that one button.
Manually launching with other methods works, but are more involved and slow down the iteration process compared to simply clicking launch in the editor.