firefox.apk won't install on my tablet

hi.

I used tablet 'a', installed firefox on it. Then made a backup (using Astro) of its apk. Then copied this apk to tablet 'b' and pressed it to install. The installation began- then after a few runs of the green installation bar a message appears "App not installed".

What is it and what can I do?

(I just wanted to note that most other apps are totally fine).

thank you