It would be great to be able to match the built in PDF editing tools that Microsoft Edge has, specifically the highlighting and drawing tools. This is one of the reasons I can't use Firefox for working with PDFs.
I think it is important to make the PDF documents opens faster, i noticed it is taking a bit longer than any browser to open a PDF File, Also it needs some important tools like a Highlighter and text box, because whenever I want to highlight something i have to use another browser that support these features.
It would be nice if you will add some functions to your PDF viewer in Firefox, which can be usefull to edit some forms, add some signs or add some drawings like Microsoft Edge. Clean PDF viewer with editing forms in PDF is not all which i want to use, because i want show or edit at once without installing external software. Microsoft Edge makes here great job, please Mozilla make your PDF viewer much better!