See also:
-Are they any different then other big sites in terms of surveillance? What information can they collect about my computer?I am personally not into the business of vetting any services for trustworthiness of their policies. Too many aspects. Too opinion based. Endless debates. Whonix unspecific.
-Are there any specific security measures that one should use while working with huge e-mail providers?No need to act differently. See any promised by security by policy as a bonus that is not to be relied upon.
-I need to enable JavaScript to access those sites. How dangerous is this?There is a lot javascript enabled vs disabled security discussions already.
-Would it add risk to use built-in e-mail programs like Icedove?I am not aware of any security comparison of Tor Browser vs Icedove with Torbirdy.