Why does Firefox itself change the file path?

Question

css

And so, I work, I don’t touch anyone, on the main page there is a picture with
img/shutterstock_336992036.jpg
After 5 minutes of work, this path turns into

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC

How is that at all?
The problem is ONLY in Mozilla. Worked in chrome and didn't see this.