Keyboard to eventually fail and there is no warning when they do. Try a different keyboard and test if it still happens.

You can try to modify this pref on the about:config page.

• browser.backspace_action = 2

You can consider to modify mouse*action prefs.

0 means "Do nothing"
1 means "Scroll contents"
2 means "Go back or forward in the history"
3 means "Zoom in or out the contents"

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

Value was (default) set to "0". which means it'll do nothing? Not what I observe I think I'll try buy a new keyborg

What pref are you talking about?

If this is browser.backspace_action then its value should be 2 to disable this feature. The list posted further down in the reply applies to mouse*action prefs.

This is what I found when opening about:config. I have changed nothing!

Sorry - forgot to attach screendump

With the default setting of zero you will go backwards in the Tab history when you press the backspace key when you are not in a text input area (or if Firefox thinks that you aren't). You can double-click the browser.backspace_action line and modify the value to 2 to see if that has effect.

My problem is still there. I've changed keyboard, I've reconfigured to all setting in browser.backspace_action but nothing helps. What I observe is; mostly when filling text in a form (like this window) it suddenly by itself go back to the previous screen. A few times it also happends just looking at a page, without any kind of keyboard activity.