Unable to save screen capture as PDF using fireshot

I use Fireshot on my Mac to take screenshots and normally save as PDF. This works fine using Safari and Chrome browsers. However, using Firefox, when saving the screenshot as a PFD it uses file type 'All files' Up till now, I have been unable to open the file saved as an 'All files' document. But this morning, saving the capture as a PDF 'All files' type, has saved the document as a PDF.

QUESTION: Just using Firefox, why does saving a screen capture uses 'All files' when saving as a PDF. And has the issue been noted and resolved, but the All files file type still shown? NOTE: The drop-down arrow on Format does not offer any alternative.