It's the exact equivalent extension of "‪Copy Link Text‬ by superevilmegaco.com‏" for chrome.
It's a very handy extension that helps you copy specified text, depend on where you click.
It can copy with single click one sentence or whole page text, or Instagram account bio.
If Firefox just lets you right-click 'scroll bar' area will be much helpful for certain tasks like bulk copy text from popup window, but you can right-click 'scroll bar' area & then hit Shift-F10 to bring context menu and then click 'Copy Element's text' extension.
This extension need little enhancement when copy certain text like 'Instagram account bio' the text should be more organized like source, not patched all together.

Helped me copy text from YouTube subitles. Very useful.