[mmooss]

Many URLs start with http(s): and end in .pdf. If we define web browser as http browser rather than html browser, then viewing PDFs fits the concept. My web browser also displays plain text, video, audio, etc., so http browser seems accurate and html browser plainly inadequate.

And regardless of logical fit for geeks (who understand the paragraph above), users clicking a .pdf URL may find it much more convenient if it just opens in their browser like any other http page, rather than downloading, opening in another window, getting lost between the MDI browser and separate SDI of the PDF file, etc. Why not treat PDF as just another web format?

To me, more strange is Firefox adding PDF editing features to its core, rather than as add-ons. Users can't edit HTML or any other media without extra tools. Many pdf reader apps can't do some of these things (afaik). Why invest developer time in PDF editing?

[OkayPhysicist]

Users absolutely can edit HTML/CSS/JS without any other tools. That's what the entire dev-tools section of the browser is about.

[mmooss]

Dev tools are not for 99% of end users and not realistically available to them (even if they stumble across dev tools, they don't know what they've found or how to use them). PDF editing is for end users and is realistically available.

[OkayPhysicist]

That seems like all the more reason it's worthwhile. If they're going to invest in the tools for 1% of their users, why wouldn't they invest in tools for 50% of their users?