Great, thank you for bringing this back! The original context menu item was needlessly removed from Firefox. The popup could look a little more modern, but that's just optional fluff. The important stuff is there now and that's what matters.
Update: Popup looks great now!

2.The "View Image Info..." item does not appear in the context menu for linked images

Edit: #2 example is upper left corner firefox icon in this page(or, https://news.daum.net/ranking/popular).
xIFr(https://addons.mozilla.org/en-US/firefox/addon/xifr/) addon support both features.

Edit2: Thanks for "Last modified:" feature in v1.5.

Following the further dumbing down of Firefox by the removal of 'View Image Info' in the right click context menu of v87, I am pleased to say that this extension makes a very good replacement.