As you have seen, Firefox for Android should automatically adjust itself depending on whether you have a physical menu button. On devices with a physical button (e.g. Galaxy S3) the on screen menu button is not shown. On devices without a physical button (e.g. Nexus 4) the on screen button is shown.

The Kindle Fire is not an officially supported device (even on stock rom) so I'm assuming there is some quirk on that device or your rom that is causing the issue.

I've tried to find a method for forcing Firefox to show the button even when it thinks that there is a physical button available. My guess is that there should be a setting in about:config somewhere but I've been unable to find it or any reference to people trying to do the same thing online.

Unless anyone else comes back with an answer I suggest trying one of the following:

Try settings here to force on screen menu buttons to appear: http://brandtkrueger.wordpress.com/2013/04/23/enable-on-screen-android-navigation-buttons-on-the-galaxy-s3-requires-root/

Try 3rd party on screen menu app. Like this one: https://play.google.com/store/apps/details?id=opotech.virtualbuttonbar&hl=en

I hope that helps.

thanks Eddy, I'll have a look at that when I get home. being an android noob hurts my head at times. I'll let you know how I get on. thanks again

Edit: I used a 3rd party menu button and options work fine. thanks again

Great! Glad to hear it worked.

Thanks for using Firefox :)

I had the exact same issue after updating my N2A Nook HD+ units from Android 4.1 to version 4.2.2.

The solution that worked for me was to go to : Settings > INTERFACE - System > Hardware Keys > ADDITIONAL OPTIONS - Show Action Overflow > selected the check box.

Apparently the update on my device cleared that box. Menu now shows up as expected.