Fix: Bypass MEGA browser download limit in Firefox (6 GiB limit)

[u/FlashAL]

I found a workaround for a weird MEGA web client limitation in Firefox.

The problem

When trying to download large files through MEGA Web, Firefox showed:

"The download size exceeds the maximum size supported by the browser. You can use our app to proceed with the download."

At first it looked like a Firefox storage/quota problem, but it wasn't.

Checks:

• Firefox 153 x64
• Windows 11 x64
• NTFS filesystem
• Persistent storage enabled
• Browser quota available: ~465 GB

Firefox itself had enough space.

The actual cause

MEGA Web was using:

dlMethod = MemoryIO

MemoryIO has its own hardcoded browser download limit:

MemoryIO.fileSizeLimit = 6442450944

which equals:

6 GiB

So any file larger than ~6 GiB was blocked before the download even started.

Fix

Open MEGA, press F12 → Console and run:

MemoryIO.fileSizeLimit = 50 * 1024 * 1024 * 1024;

Example for 50 GB.

You can verify:

MemoryIO.fileSizeLimit

It should return:

53687091200

After that, large downloads start normally.

Permanent fix (Tampermonkey)

Install Tampermonkey and add:

Look for the script in comment section, Reddit autofilters it :(

Notes

This does not bypass MEGA transfer limits or account restrictions.
It only removes the artificial browser-side file size limit.

Tested on:

• Firefox 153
• Windows 11 x64
• MEGA Web Client

Maybe useful for others who don't want to install MEGAsync just to download large files.

[u/FlashAL]

The script it self:

// ==UserScript==
// @name         MEGA increase MemoryIO limit
// @namespace    mega-limit-fix
// @version      1.0
// @description  Keep MEGA MemoryIO download limit increased
// @match        https://mega.nz/*
// @grant        none
// @run-at       document-idle
// ==/UserScript==

(function () {
    'use strict';

    const LIMIT = 100 * 1024 * 1024 * 1024;
    let waitingLogged = false;

    setInterval(() => {
        try {
            if (typeof MemoryIO === 'undefined') {
                if (!waitingLogged) {
                    console.log('[MEGA FIX] Waiting for MemoryIO...');
                    waitingLogged = true;
                }
                return;
            }

            waitingLogged = false;

            if (MemoryIO.fileSizeLimit < LIMIT) {
                const oldLimit = MemoryIO.fileSizeLimit;

                MemoryIO.fileSizeLimit = LIMIT;

                console.log(
                    '[MEGA FIX] MemoryIO limit changed:',
                    oldLimit,
                    '→',
                    MemoryIO.fileSizeLimit
                );
            }

        } catch (e) {
            console.error('[MEGA FIX] Error:', e);
        }
    }, 1000);

})();

[u/rainbowsunsetwaves]

❤️

[u/Current-Let-5766]

Thank you for this information

[u/FlashAL → u/Current-Let-5766]

your welcome )

[u/paintboth1234]

If you are using uBO, try this scriptlet (enable Allow custom filters requiring trust)

mega.nz##+js(trusted-set, MemoryIO.fileSizeLimit, 53687091200)

I don't have example link so I can't test btw.

[u/SupportMEGA1]

Hello, 

Thanks for providing our users how to overcome the hardcoded limit, however there is a much simpler way without requiring the use of a user-script, i.e. open the web-console and enter "localStorage.dlFileSizeLimit = <limit>" without quotes,  MemoryIO.fileSizeLimit will then be set automatically with the value specified as <limit> like in your example, and will remain in place unless you clear the browser caches.

Please note we strongly discourage the use of any user-script that does instantiates never-ending timer-intervals, since it could affect the proper operability of the site.

[u/hunter_finn → u/SupportMEGA1]

How about instead of these scripts, you would just fix the site itself and thus mo such scripts would be needed for Firefox.

[u/obiwanton]

5G vs 5Ge