I gave Firefox a chance as my PDF reader as it has a pretty efficient engine. But that didn't work out as I don't need to read PDFs often so every time it launched, it ran an update that added 10s to reading the PDF... :/
My current main browser across desktop and mobile is Brave. Pretty happy with it. Overall more efficient and with a better UI than FF. I've used FF for many years, but I feel it's simply not as good as competitors anymore.
If you're going to use a Chromium based browser, why pick one that's filled with crypto ads? I use Firefox on mobile because it supports extensions. One of the main benefits of the web is that, unlike proprietary native apps, I get to experience it the way I want. The web is nearly intolerable without extensions.
Generally speaking most dedicated PDF readers haven't implemented the nastier parts of the PDF spec that need a sandbox. Except adobe. They support everything because they wrote it. But they keep making it worse so I can't recommend them.
My current main browser across desktop and mobile is Brave. Pretty happy with it. Overall more efficient and with a better UI than FF. I've used FF for many years, but I feel it's simply not as good as competitors anymore.