ATTN: Hotfix for broken embedded forms in Firefox 46 (release date April 19)

Warning! On the near horizon is a version of Firefox that will break embedded forms.  As I noted in Firefox Developer Edition​, Firefox 46 -- already in-the-wild for folks using Firefox Developer Edition -- is moving into Beta on March 8 and will be released worldwide via auto-update on April 19.

Luckily, your faithful forms guy has a fix you can put in place now to avoid disruption.  Add the following style either in a <style> tag or via an external stylesheet.  If you use an external stylesheet, make sure it loads before forms2.js/forms2.min.js.

#MktoForms2XDIframe {
    visibility: hidden;
    position: absolute;
    display: block !important;
}

• The breakage affects forms using the embed code. It does not affect native form objects on Marketo-hosted LPs, but it can affect forms loaded as embeds (in HTML blocks) on Marketo-hosted pages. If you are not sure which method you use, apply the fix.
• Marketo Support has been made aware of the issue but has not planned an official fix.
• The change is related to Gecko's reinterpretation of the CSSOM getComputedStyle method. It should be noted that Chrome and IE are not planning to use the same interpretation.
• If you want more details you can DM me.