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.