As commented out, this is a Firefox debugging tool that displays whitespace between elements that have
display: inline by default, since spaces between these elements are treated by browsers as spacing. See the example below:
By default, the buttons display
inline , however there is a line break (which is a whitespace ) between them, so the Firefox inspector displays this symbol indicating the line break :
<img src="http://lorempixel.com/100/100"/><imgsrc="http://lorempixel.com/100/100" />
Now, if the images on the same line are defined, the spacing ceases to exist. Usually we do the first form, because the code is more readable, but since we do not define CSS, we do not expect such a spacing. In this way, the Firefox inspector helps us find the source of this behavior.
If you set the buttons on the same line, you will see that the inspector does not display this character:
The spacing will still exist because it is the default button style.