in src/content_script.js [193:207]
function buildInpageIframe(socialAction, fbcIframeHeight) {
const iframe = document.createElement("iframe");
iframe.src = browser.runtime.getURL(`inpage-content.html?action=${socialAction}`);
iframe.width = 350;
// This height is derived from the Figma file. However, this is just the starting instance of the iframe/inpage menu. After it's built out, it resizes itself based on the inner contents.
iframe.height = fbcIframeHeight;
iframe.title = browser.i18n.getMessage("facebookContainer");
iframe.tabIndex = 0;
iframe.ariaHidden = "false";
iframe.id = socialAction;
iframe.classList.add("fbc-content-box");
return iframe;
}