mj-group are not behaving as they should in preview mode on small device

To Reproduce

Build a mj-group with two columns
Use the responsive tool : columns will stack on each other on small screens.

Expected behavior They should stay on the same row. It's work on the HTML output, but not on the preview

First clue the previewer is adding a .moz-text-html class around the responsive class. In the MJML plugin, this class is supposed to be for thunderbird email client.

<style>
    .moz-text-html .mj-column-per-50 {
        max-width:50%;
        width:50% !important;
    }
</style>

Didn't found yet where to remove this class. Maybe it comes from the grapesJS-mjml config, but I don't know where...

GrapesJS / mjml

mj-group are not behaving as they should in preview mode on small device #241