via mastodon: Implementing form filling and accessibility in the Firefox PDF viewer - Mozilla Hacks - the Web developer blog — https://hacks.mozilla.org/2021/10/implementing-form-filling-and-accessibility-in-the-firefox-pdf-viewer/

This appears to mean that Firefox on Linux can open and fill those pesky Canadian Government forms that were created with Adobe Livecycle. These used to appear as "Please wait... If this message is not eventually replaced by the proper contents of the document, your PDF viewer may not be able to display this type of document." but now open as proper forms.

This must have been non-trivial to implement, because even Adobe couldn't create XFA forms outside the Windows-only Livecycle.

cheers,

 Stewart