Tiled Mosaic galleries breaking layout in Firefox

Jetpack’s Tiled Galleries (and other embeds) will indeed respect the $content_width value.

I’d suggest declaring multiple $content_width values depending on the page template to accomodate the different layouts available in your theme.

Here is an example that should help you:
https://davejesch.com/wordpress/wordpress-tech/variable-width-pages-for-your-theme/

Hey Jeremy,
Thanks for the tips. While useful, im afraid this doesn’t solve my issue because the problem is not with different pages but different with of the same page as it decreases for smaller devices. Essentially im looking to making the gallery responsive.

Essentially im looking to making the gallery responsive.

You should be able to make that happen with CSS, by defining a maximum width for the gallery container (or the whole content container). This article explains things in details:
https://css-tricks.com/css-media-queries/

You can also look at how the Twenty Fifteen theme is built to find out more. Here is an example of a tiled gallery in Twenty Fifteen:
https://twentyfifteendemo.wordpress.com/2011/07/07/gallery-post-format-example/

Thanks Jeremy,

For some reason on my layout here I had to declare a max-width, nothing else worked.

This layout is based on flex box btw, that might have some relation to this as I’ve not had any problems with the gallery before.

Thanks again.