Every time I let my phone display turn off, and then unlock it and return to Firefox, or just go to another app or hit my home button and then go back to Firefox, it's showing its Mozilla tab. That's the one that lists the following items: About Firefox, FAQs, Give feedback, Show product announcements, Telemetry, Crash Reporter, and Firefox Health Report. I can hit the back button on my phone and get back to whatever page it was viewing, but then as soon as I leave and come back, that list is up again. I'm using Android version 2.3.6 and Firefox version 32.0.3 on a MyTouchQ phone.
I think this question here on the Mozilla Support site is a similar problem to yours: https://support.mozilla.org/en-US/questions/1013146
Otherwise...try uninstalling/re-installing the app. Also...you could always download a different browser.