User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36 Steps to reproduce: Debugging a Vaadin application using GWT SuperDevMode, which provides a source map for the original Java files Actual results: Fetched sourcemap JSON contains "version":3, "file":"sourceMap", "lineCount":171409, "sourceRoot":"http://localhost:9876/sourcemaps/com.vaadin.DefaultWidgetSet/", "mappings": ... Firefox debugger shows the sources as * 127.0.0.1:9876 (correct) * sourcemaps/com.vaadin.DefaultWidgetSet/http://127.0.0.1:9876/sourcemaps/com.vaadin.DefaultWidgetSet When trying to open a Java file in the debugger, a server requests is sent for /sourcemaps/com.vaadin.DefaultWidgetSet/http:/127.0.0.1:9876/sourcemaps/com.vaadin.DefaultWidgetSet/com/vaadin/client/ui/FocusUtil.java which obviously returns a 404 because the URL is wrong This is with the latest update of Firefox Developer Edition (54.0a2) Expected results: The absolute URL should be used. Debugger should show the correct URL instead of an absolute URL somehow appended to a relative URL with one slash removed. Opening a Java file in the debugger should make a correct request and show the sources. In Firefox 53.0, everything works as expected.

Seems substantially the same as bug 1355126.