Where was it before? Been using Firefox non stop for 20 years but last time I went to the website was probably when I still used Windows XP.
I always liked https://ftp.mozilla.org/pub/firefox/releases/ but that's not the primary consumer page.
Even an older iPad can run Netflix and Plex and maybe a couple of other streaming apps. You should be able to use it for Spotify and definitely Apple Music.
Adobe Viewer (? not sure of the name) was the only adobe product that had this ability afaik, and while I managed to get an old exe, it's been discontinued unfortunately.
The closest appears to be Xodo PDF with pretty much all features, but it has a ton of popups.
[1]: https://www.adobe.com/devnet-docs/acrobatetk/tools/Wizard/in...
[2]: https://www.adobe.com/devnet-docs/acrobatetk/tools/Wizard/on...
[3]: https://www.adobe.com/devnet-docs/acrobatetk/tools/AdminGuid...
[4]: https://www.adobe.com/devnet-docs/acrobatetk/tools/PrefRef/W...
No one has to download Edge or Safari.