Original problem: Firefox 70.0-1 amd64 doesn't display JPEG image thumbnails in the file upload dialog (a default system dialog) for images with filesize > ~1.7 MB. For small images everything works as expected.

Desired behavior: I want Firefox to display thumbnails in the file upload dialog for all the images regardless of its size, or at least increase the default limitation.

I've learned that behind the scenes Firefox uses GTK FileChooser to interact with me. I've run through FileChooser source code and learned that it uses libegg to generate a thumbnail.

I tried to read the code for thumbnail generation (+ header file), but it doesn't help me. Either I'm not good enough in reading C (which I'm not), or there is no such limitation in this place.

Any hint how to fix that behavior? Is there any setting to tune or anything at all?


Turns out firefox uses its own mechanism for previews and indeed the limitation by image size is hardcoded there (only images < 4096px).

The code.

The limitation is introduced due to this bug

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