I have the same issue on windows 10 64-bit with firefox 58. I wanted to see if anybody has experienced anything similar or if Mozilla are aware of this. Testing with both Firefox 57 X86 and X64 on the same machine gives me the same result. When testing with several different Windows 7 configurations, whilst there are some issues that need to be addressed by Mozilla separately I am successfully able to navigate around web pages as expected. I'm aware that huge changes have been made to the internal functionality of the latest release, but it was hinted that this would only cause slowness and not complete degredation of the browsing experience. I've ensured that the 'Prevent accessibility services from accessing your browser' checkbox is unchecked when this is ticked, nothing at all reads so I can definitely tell that this is not the issue. Reading the content of editable fields (including the Address Bar) works without issue, but all other interaction results in the behaviour outlined above. When using the latest NVDA snapshot (next-14617,ef52ddc4) in combination with Windows 10 (3 Build 15063) and the latest version of Firefox (57 X64), NVDA is literally unusable and results in the word 'unknown' being output whenever I tab around the window.

Firefox and windows 10 issues