Slow and abnormally lagging GM.xmlHttpRequest

[AlttiRi]

I have noted about this in this comment, but I think it's better to create a separate issue.
Also the similar behaviour was in VM, but it was fixed recently.

Expected Behavior

Downloading with GM.xmlHttpRequest of "big" files works fast, without any lag or freezing.
ViolentMonkey (the latest version) downloads a 100 MB almost instantly (as soon as all data were received from a server).

Actual Behavior

Downloading of a 100 MB file leads to a lags for 6 second + for 10 the page is totally frozen. (16 seconds of total)

Specifications

• Chromium: 85
• TM: 4.12.6123 (Beta)
• OS: Win10

Script

// ==UserScript==
// @name        Issue 1107 (GM.xmlHttpRequest, 104 MB, gfycat.com)
// @namespace   Issues
// @match       https://github.com/Tampermonkey/tampermonkey/issues/1107
// @match       https://example.com/
// @grant       GM.xmlHttpRequest
// @connect     giant.gfycat.com
// ==/UserScript==

!async function() {
    console.log("downloading (104 MB)...");
    const response = await new Promise((resolve, reject) => {
        GM.xmlHttpRequest({
            method: "get",
            url: "https://giant.gfycat.com/ConfusedRecentGuppy.mp4", // 104 MB
            responseType: "blob",
            onload: resolve,
            onerror: reject,
        });
    });
    console.log("response:", response);

    const {response: blob} = response;
    downloadBlob(blob, "ConfusedRecentGuppy.mp4");
}();

function downloadBlob(blob, name) {
    const anchor = document.createElement("a");
    anchor.setAttribute("download", name || "");
    anchor.href = URL.createObjectURL(blob);
    anchor.click();
}

[AlttiRi]

Install this script, reload this page, and try to select different parts of a text, you will see the lags (~1 fps) and the page freezing for some time until the file is downloaded (saved).
You can also try this with less sized file (32 MB): https://giant.gfycat.com/ShockedSecondaryFiddlercrab.mp4

---

Note: the lags (freezing) start after the file downloading was complied in the background script (when the data transmit will be started from the background script to the content script).

[derjanb]

Duplicate of #279

Please see #279 (comment) for more information.

[AlttiRi]

The script does not work at all with 4.12.6124. File is not saved.

UPD: only on github.com due to CSP.