I've been thinking about your problem. In my opinion, there is a problem in your phone, not in the browser. Have you tried to root your phone in the last days or weeks? In my opinion there is a problem in you not being able to run recovery mode. Couldn't you have received virus from somewhere?

Thank you very much! :)

No problem with my phone, as it has also happened to my tablet eith stock firmware.

I think that isn't problem in Firefox browser. It's only my opinion. Were you able to give mobile phone or tablet into recovery mode?

No im not able to, both devices experienced the same problem after firefox error report popped up, it was the browser cousing it.

http://forums.whirlpool.net.au/archive/2275765. A link of someone who also has experienced this. This is very major, mozilla releasing applications that bricks phones.

Firefox is an Application. It has no bearing on the Android OS being able to boot. Programs from the Play Store are not able insert themselves into the boot process of Android. If you find a way to do this then you can a nice security bounty from Google.

The whirlpool messageboard makes no mention of Firefox for Android.

Mozilla Firefox did not cause your phone to become unbootable.

Then I opened up the Firefox browser and before I could navigate to any site, it froze and became unresponsive. I shut it down by holding down the power button. It then rebooted and loaded into a screen with the android logo and "Downloading, do not turn off target". I left it for a while (maybe half an hour) and it didn't seem to progress past this screen. That same quote happened to me. I explain again my phone isnt rooted, it has official touch wiz nothing changed, then that happened to my S4. Not knowing what happened I grabbed my brand new note 10.1 with stock apps, download firefox started browsing and the same thing happened.