For me, not being in the browser is a feature, not a bug. I often want to be able to open a PDF in a dedicated window I can easily switch to.

The problem with PDF is that it's a bag of needles disguised as a piece of paper. Most of the time people expect a PDF to be a document, not a Form, Rich Media, Contract, Javascript, or any of the other crap it can do. All that extra crap dramatically increases the attack surface area of Acrobat or any other PDF reader that supports it.

At least the PDF reader in Firefox is a Javascript App that runs in a Browser sandbox and doesn't support 99% of the crap a PDF can do.

Sure, but you can open a PDF in a new browser window. I'd rather not broaden my trusted codebase by installing another PDF reader.

OSs have this annoying habit of condensing multiple windows of a single application down to one taskbar item/dock item/whatever.

On Windows this can easily be remedied in the options accessible via the taskbar. I always turn this off and tell it to show the full window titles instead of just the icons. Windows are not browser tabs, I don't ever have enough of them open to need that stacking behaviour.

Another option for Chrome/Windows is to open a Guest window or an Incognito window, which is treated as a separate window-group.

Too late to edit: I see now that only a Guest window gets its own window-group. Incognito windows do not.

What is the difference between having multiple pdf reader windows vs multiple browser windows then? If you are on a mac: cmd+` is your friend.

I only have one PDF window open.

But do they remember your position in the PDF between restarts? I some times read books or lecture notes in PDF format, and dedicated programs works much better for that than the support in browsers

Not Safari.

How so? I have no problem opening PDF links directly in Safari.

Safari "supports PDF", but not well. The PDF viewer is run in an extremely janky view that clearly has not been updated in years. It runs out-of-process, but takes little advantage of the many advances in XPC rendering that have come in recent years; as such it cannot handle looking up services correctly, or vibrancy, or even have Retina support for its UI. And those are just visual: the PDF support itself is shoddy; it's unable to do many things that other browsers can do out-of-the-box (forms?), searching for text has been broken for the better part of a year. It's an obvious rough spot in Safari's otherwise polished interface.

Fair criticism. I guess my bar for what I define as "good PDF support" is much lower than yours - I only generally read them or plug in a digital signature when signing my lease.

Personally, I am loath to download documents. I actually like what iOS Safari does, which is run the generic document previewer on files inside the app itself. I hate clicking on a link on my computer and then getting a PPTX that I have to open in PowerPoint.