Solved by using an old google account link.

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems.

With the new Gmail update, Firefox 27.0.1 no longer allows me to sign into my account, as it says my browser does not support Javascript. Is there any method or add-on I can use to enable Javascript on my old Firefox version? I tried using about:config, but I forgot my password and cannot log in.

JavaScript should be enabled by default unless you have some extension(s) that can deal with JavaScript like NoScript etc.

Btw unless you are using mobile Firefox for iOS devices (iPad, iPhone) the Firefox 27.0.1 was released way back on February 13, 2014. https://www.mozilla.org/firefox/releases/