Google killed the View Image button recently and while it's easy enough to work around, it'd be even better if there was a way to restore it. Hang on... isn't that what browser extensions and addons are for?
I doubt Mozilla cares about the addon, but I'm a little surprised it survived Google's review process for the Web Store. Maybe the company will wait until someone from Getty kicks up a fuss (if that ever happens).
And even if it did, it won't magically delete the extension off your hard drive.
If you're worried about it doing something nefarious, the source code is freely available on GitHub. As a developer myself, I had a scan and it looks fine.