Кнопка "Собарть и запустить" не работает

[demoj1]

При клике на кнопку "Собрать и запустить" ничего не происходит, в консоль сваливается ошибка.

Бразуер:

Vivaldi	2.7.1628.33 (Stable channel) (64-bit)
Revision	3bef5abd3cc7273c4ab9932c541c37ca668f9cc0
OS	Linux
JavaScript	V8 7.6.303.30
Flash	(Disabled)
User Agent	Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.137 Safari/537.36 Vivaldi/2.7.1628.33
Command Line	/usr/bin/vivaldi-stable --flag-switches-begin --flag-switches-end --disable-smooth-scrolling --save-page-as-mhtml
Executable Path	/opt/vivaldi/vivaldi
Profile Path	/home/dmr/.config/vivaldi/Default

Под Firefox (69.0 (64-bit)) то же самое

browser log

fsharplang.ru/:12 GET https://fonts.googleapis.com/css?family=%7FSegoe%20UI net::ERR_ABORTED 400
content.min.js:2 [Deprecation] Element.createShadowRoot is deprecated and will be removed in M80, around February 2020. Please use Element.attachShadow instead. See https://www.chromestatus.com/features/4507242028072960 and https://developers.google.com/web/updates/2019/07/web-components-time-to-upgrade for more details.
(anonymous) @ content.min.js:2
(index):1 Unchecked runtime.lastError: The message port closed before a response was received.
(index):1 Unchecked runtime.lastError: The message port closed before a response was received.
(index):1 Access to XMLHttpRequest at 'http://rextester.com/rundotnet/api' from origin 'http://fsharplang.ru' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
(index):386 Uncaught TypeError: warningsBox.clear is not a function
    at Object. ((index):386)
    at i (jquery.min.js:2)
    at Object.fireWith [as rejectWith] (jquery.min.js:2)
    at A (jquery.min.js:4)
    at XMLHttpRequest. (jquery.min.js:4)
(anonymous) @ (index):386
i @ jquery.min.js:2
fireWith @ jquery.min.js:2
A @ jquery.min.js:4
(anonymous) @ jquery.min.js:4
error (async)
send @ jquery.min.js:4
ajax @ jquery.min.js:4
(anonymous) @ (index):367
dispatch @ jquery.min.js:3
q.handle @ jquery.min.js:3
VM16:1 POST http://rextester.com/rundotnet/api net::ERR_FAILED
(anonymous) @ VM16:1
send @ jquery.min.js:4
ajax @ jquery.min.js:4
(anonymous) @ (index):367
dispatch @ jquery.min.js:3
q.handle @ jquery.min.js:3