Unable to download
Could you download to a blackberry playbook? Anything?
Alla svar (1)
Mozilla only has Firefox for desktop Windows, Mac OSX 10.9+, and Linux www.mozilla.org/firefox/all/ and for Android and the Firefox shell for iOS.
The old PlayBooks used the BlackBerry Tablet OS (QNX) 2.1 OS as it did not use Android. Even if it did use Android it would be a rather old version now. https://en.wikipedia.org/wiki/BlackBerry_Tablet_OS
It was possible to side load some Android 2.3 applications as I did in past with some games on one of my two PlayBook's, a 32Gb and 64GB.
It also does not help that support for QNX has long been removed from the Mozilla source tree.
In past some were able to side load some Android versions of Firefox onto BB10 but it is not without issues. BlackBerry of course never ported BB10 for PlayBook as was promised.