Also tried run as administrator and compatibility modes.

Try using the full, offline installer package from here. https://www.mozilla.com/en-US/firefox/all.html

Thank you for reply but that's for regular Firefox, this is about Firefox dev (developer edition).

Here it is: https://www.mozilla.org/en-US/firefox/developer/all/

See also the CDN server:

• http://download.cdn.mozilla.net/pub/mozilla.org/firefox/nightly/latest-mozilla-aurora/

Thank you guys, downloaded, but got the same error. Damn.

Update: I restarted comp in safe mode and did successful installation from there. Works fine.