javascript injected in tinymce editor by wordpress when gutenberg is desactivated

Question

with a fresh install and up to date of wordpress (5.8.2), when I desactivate gutenberg editor, Wordpress add this javascript code in all TinyMCE editor (content, acf fields etc..) I have no plugin and theme by default. I desactivate Gutenberg with code or with a plugin, no changes. Anyone have a tip ? thx

<script type="text/javascript">
var spector;
var captureOnLoad = false;
var captureOffScreen = false;
window.__SPECTOR_Canvases = [];

(function() {
    var __SPECTOR_Origin_EXTENSION_GetContext = HTMLCanvasElement.prototype.getContext;
    HTMLCanvasElement.prototype.__SPECTOR_Origin_EXTENSION_GetContext = __SPECTOR_Origin_EXTENSION_GetContext;

    if (typeof OffscreenCanvas !== 'undefined') {
        var __SPECTOR_Origin_EXTENSION_OffscreenGetContext = OffscreenCanvas.prototype.getContext;
        OffscreenCanvas.prototype.__SPECTOR_Origin_EXTENSION_OffscreenGetContext = __SPECTOR_Origin_EXTENSION_OffscreenGetContext;

        OffscreenCanvas.prototype.getContext = function () {
            var context = null;
            if (!arguments.length) {
                return context;
            }

            if (arguments.length === 1) {
                context = this.__SPECTOR_Origin_EXTENSION_OffscreenGetContext(arguments[0]);
                if (context === null) {
                    return context;
                }
            }
            else if (arguments.length === 2) {
                context = this.__SPECTOR_Origin_EXTENSION_OffscreenGetContext(arguments[0], arguments[1]);
                if (context === null) {
                    return context;
                }
            }

            var contextNames = ["webgl", "experimental-webgl", "webgl2", "experimental-webgl2"];
            if (contextNames.indexOf(arguments[0]) !== -1) {
                // context.canvas.setAttribute("__spector_context_type", arguments[0]);
                // Notify the page a canvas is available.
                var myEvent = new CustomEvent("SpectorWebGLCanvasAvailableEvent");
                document.dispatchEvent(myEvent);
                this.id = "Offscreen";
                window.__SPECTOR_Canvases.push(this);

                if (captureOnLoad) {
                    // Ensures canvas is in the dom to capture the one we are currently tracking.
                    if (false) {
                        spector.captureContext(context, 500, false, false);
                        captureOnLoad = false;
                    }
                }
            }

            return context;
        }
    }

    HTMLCanvasElement.prototype.getContext = function () {
        var context = null;
        if (!arguments.length) {
            return context;
        }

        if (arguments.length === 1) {
            context = this.__SPECTOR_Origin_EXTENSION_GetContext(arguments[0]);
            if (context === null) {
                return context;
            }
        }
        else if (arguments.length === 2) {
            context = this.__SPECTOR_Origin_EXTENSION_GetContext(arguments[0], arguments[1]);
            if (context === null) {
                return context;
            }
        }

        var contextNames = ["webgl", "experimental-webgl", "webgl2", "experimental-webgl2"];
        if (contextNames.indexOf(arguments[0]) !== -1) {
            context.canvas.setAttribute("__spector_context_type", arguments[0]);
            // Notify the page a canvas is available.
            var myEvent = new CustomEvent("SpectorWebGLCanvasAvailableEvent");
            document.dispatchEvent(myEvent);

            if (captureOffScreen) {
                var found = false;
                for (var i = 0; i < window.__SPECTOR_Canvases.length; i++) {
                    if (window.__SPECTOR_Canvases[i] === this) {
                        found = true;
                        break;
                    }
                }
                if (!found) {
                    window.__SPECTOR_Canvases.push(this);
                }
            }

            if (captureOnLoad) {
                // Ensures canvas is in the dom to capture the one we are currently tracking.
                if (this.parentElement || false) {
                    spector.captureContext(context, 500, false, false);
                    captureOnLoad = false;
                }
            }
        }

        return context;
    }
})()</script>

Answer 1

It is very likely added by the Spector.js extension : same behaviour with the Spector extension enabled on Firefox (when switching editor, or after save) => disabling the extension solved the issue.