Does opacity:0 have exactly the same effect as visibility:hidden

Here is a compilation of verified information from the various answers.

Each of these CSS properties is unique. In addition to rendering an element not visible, they have the following additional effect(s):

1. Collapses the space that the element would normally occupy
2. Responds to events (e.g., click, keypress)
3. Participates in the taborder

                     collapse events taborder
opacity: 0              No     Yes     Yes
visibility: hidden      No     No      No
visibility: collapse   Yes*    No      No
display: none          Yes     No      No

* Yes inside a table element, otherwise No.

No.

Elements with opacity create new stacking context.

Also, CSS spec doesn't define this, but elements with opacity:0 are clickable, and elements with visibility:hidden are not.

No it does not. There is a big difference. They are similar because you can see through the element if visibility is hidden or opacity is 0, however

opacity: 0 : you can not click on elements behind it.

visibility: hidden : you can click on elements behind it.