How about Sumatra PDF?
ETA: I think it's open source.
this post was submitted on 09 Jan 2026
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Came here to suggest SumatraPDF as well
How to open it's UI in browser ?
Sorry I missed that part. I don't know if it has that functionality.
Why do you need it to be a browser plugin, a program that embeds itself into the webbrowser?
Firefox does have PDF view and edit with section jumping, comments, and highlighting. What do you mean by “easier”? What's easier than a sidebar table of contents, and a toolbar with highlighting and comment actions? I don't see what could be “easier” than that.
it is a native app. https://github.com/sumatrapdfreader/sumatrapdf
It is the most performant pdf viewer on windows (that i know of). it uses libmupdf
ETA: I think it’s open source.
It is: https://github.com/sumatrapdfreader/sumatrapdf/blob/master/COPYING
Why not just let Firefox open the PDF? It will read them on its own. Is it missing a feature you need?
I need a more powerful PDF viewer with easier jumping to sections, comments, and highlighting.
https://programming.dev/post/39695120
Some person on the fediverse has made an open source PDF editor... their other posts say its browser based. I haven't tried it but this seems to fit your request.
Do you need the pdf to open in Firefox/browser?
If not, PDF-XChange Editor is a pretty good advanced standalone program. It comes in free and paid versions
You want a PDF viewer that's accessible from Firefox, but you don't want to use the built in Firefox PDF viewer?
If you really need it accessible from the browser, you're probably looking at spinning up a Selkies docker container. That'll get you an entire desktop environment in a web browser.