A GIF holds at most 256 colours per frame and can be animated. JPG has no colour limit and no animation, and nearly every upload form, document editor and print shop accepts it. This converter reads each GIF in your browser and saves its first frame as a JPG by default. Switch to "Every frame" and each frame of an animation becomes its own JPG, packed in one ZIP per GIF.
Frames are rebuilt the way a browser plays the animation: when a GIF only stores the part of the picture that changed, the tool paints that change over the previous frame, so every JPG shows the full picture at that moment, not a fragment. JPG can't store transparency, so see-through pixels are filled with white, black or a colour you pick.
Limits: the JPG keeps the GIF's colours, it doesn't add detail the GIF never had, so a dithered 256-colour GIF still looks dithered. Frames past 500 in one GIF are left out, and timing between frames is lost because JPGs are still images.