Hold shift and right click on a video to open the context menu. If the element you clicked on is a video the context menu will contain the "Copy Video Frame" entity.
Note: if the entity is not shown, this means that the clicked element is either not a video element or some other (transparent) element is overshadowing it.
To get around overshadowing either the overlayed elements needs to be removed or the video needs to be brought to the front. Usually uBlock Origin's element picker or Firefox's built-in element inspector will be able to help here.
Note: if you want to directly copy the image into the clipboard (aka. skip/disable the image tab creation) you can grant the addon the optional clipboardWrite permission
Since it is not technically necessary and users might feel more comfortable knowing that the addon will not be able to access their clipboard this function is completely optional and disabled by default.
Note: DRM and CORS protected content is not extractable in the same way as other content, so a different approch is used which unfortunetly has the drawback of also capturing overlayed content and using the videos displayed size instead of its natural values.
