Fluid width?

Most Facebook social plugins do not support a 100% width. You must specify a width in whole pixels within the allowed range of the social plugin and your chosen options (e.g. button vs. box). The Comments Box social plugin has a mobile parameter to set width at 100%.

You can override the option call with your own computed width information if available. Filter on option_facebook_like_button setting width to the $content_width of the current theme for example.