Example app demonstrating that Firefox and Chrome treat relative paths differently - Firefox treats sourceURL lines in a js file as relative to the JS file, but Chrome treats them as relative to the html page which loaded the JS to begin with.
Run python -m http.server as an easy way to see the requests each browser makes.
Results in Firefox when loading /index.html ("seems to work" from my perspective):
127.0.0.1 - - [14/Jun/2019 08:33:37] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:33:37] "GET /js/all.js HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:33:38] code 404, message File not found
127.0.0.1 - - [14/Jun/2019 08:33:38] "GET /favicon.ico HTTP/1.1" 404 -
127.0.0.1 - - [14/Jun/2019 08:33:41] "GET /js/uncompiled/app.js.map HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:33:41] "GET /js/uncompiled/app.js HTTP/1.1" 200 -
Results in Chrome when loading /index.html ("seems to be broken" from my perspective):
127.0.0.1 - - [14/Jun/2019 08:34:22] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:34:22] "GET /js/all.js HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:34:22] code 404, message File not found
127.0.0.1 - - [14/Jun/2019 08:34:22] "GET /uncompiled/app.js.map HTTP/1.1" 404 -
127.0.0.1 - - [14/Jun/2019 08:34:23] code 404, message File not found
127.0.0.1 - - [14/Jun/2019 08:34:23] "GET /favicon.ico HTTP/1.1" 404 -
Example with another html file in a different directory, showing that the paths ought to be relative to the JS file, not HTML:
Firefox, working:
127.0.0.1 - - [14/Jun/2019 08:43:48] "GET /otherapp HTTP/1.1" 301 -
127.0.0.1 - - [14/Jun/2019 08:43:48] "GET /otherapp/ HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:43:48] "GET /js/all.js HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:43:49] "GET /js/uncompiled/app.js.map HTTP/1.1" 304 -
127.0.0.1 - - [14/Jun/2019 08:43:49] "GET /js/uncompiled/app.js HTTP/1.1" 304 -
127.0.0.1 - - [14/Jun/2019 08:43:50] code 404, message File not found
127.0.0.1 - - [14/Jun/2019 08:43:50] "GET /favicon.ico HTTP/1.1" 404 -
Chrome, not working:
127.0.0.1 - - [14/Jun/2019 08:44:24] "GET /otherapp HTTP/1.1" 301 -
127.0.0.1 - - [14/Jun/2019 08:44:24] "GET /otherapp/ HTTP/1.1" 200 -
127.0.0.1 - - [14/Jun/2019 08:44:24] "GET /js/all.js HTTP/1.1" 304 -
127.0.0.1 - - [14/Jun/2019 08:44:24] code 404, message File not found
127.0.0.1 - - [14/Jun/2019 08:44:24] "GET /otherapp/uncompiled/app.js.map HTTP/1.1" 404 -