Currently it only consults the list of folders in the Sublime "project" (eg., from doing File>Open Folder) when it tries to map an open file to a URL. This means if you just open a file directly, you can't set a breakpoint in it.
Two possible fixes -
When toggling a breakpoint in a file that doesn't have a mapping, attempt to use the file's path to come up with a mapping right there.
Broader change: whenever a mapping is needed, ie., whenever a break is hit -- or whenever a new file is opened -- attempt to use the open files' paths to augment the mapping table.
Currently it only consults the list of folders in the Sublime "project" (eg., from doing File>Open Folder) when it tries to map an open file to a URL. This means if you just open a file directly, you can't set a breakpoint in it.
Two possible fixes -
Workaround noted here