I had an extension called “image search for google”. Now it is missing.
In the web I could still find a link.
https://addons.mozilla.org/ru/firefox/addon/image-search-for-google/
What happened to the extension. Why it was deleted?
Most probably a malware 
. Crazy, right?
Popular “types” of extensions are often cloned, rebranded and filled with malware.
It’s best to use one with “Recommended” badge:
https://addons.mozilla.org/en-US/firefox/search/?promoted=recommended&q=image%20google%20search
If you are installing extension without the badge, make sure its author is credible (like this one ).