The short answer for a firemouth that keeps heading for the surface
A firemouth cichlid does not jump for fun. It jumps when something in the tank gives it a split-second reason to flee upward: a tank mate lunging, a net or hand appearing overhead, a sudden light change, or water that has drifted into uncomfortable territory. So the fix has two halves. First, make escape physically impossible with a complete, close-fitting cover. Second, work through the triggers, because a fish that keeps trying to leave is telling you something about life inside the glass, and a lid alone should not be the whole answer.
Why firemouths are prone to bolting
Firemouths are territorial Central American cichlids. A male defending a cave or a patch of substrate will flare and posture, and a rival or a pushier cichlid may answer by charging. The chased fish's fastest escape route is often straight up. Firemouths also startle hard at shadows passing over the tank, which reads to them as a predator from above, and at vibrations from a slammed stand door or a hand tapping the glass. Poor or shifting water adds background stress that shortens the fuse: a fish already coping with ammonia, a temperature swing after a water change, or low oxygen at the surface is quicker to panic. Crowding makes all of it worse, because a firemouth without a defensible hiding place lives permanently on edge.
Seal the tank properly, not approximately
Fit a rigid lid or a tight mesh cover that spans the whole top, then walk the perimeter looking for the gaps people forget: the cut-outs around filter inlets and outlets, the notch where heater and airline cables leave, and the feeding hatch that never quite latches. Firemouths are not huge, but a determined adult can thread a surprisingly narrow slot, especially during a chase. Cut mesh or acrylic inserts to close those openings rather than leaving them for convenience. If the tank runs open-topped for strong lighting, lower the water level a few inches as a partial buffer, but treat that as a stopgap, not a solution. After every water change and feeding, make pressing the lid fully home a habit, because most escapes happen through a cover left slightly ajar after maintenance.
Remove the triggers inside the tank
Give each firemouth broken sightlines and more than one cave or rock pile, so a subordinate fish can disappear sideways instead of launching upward. Review tank mates honestly: fin-nippers, much larger cichlids and relentless chasers do not belong with firemouths, and a second male in a small footprint invites constant sparring. Test the water and correct anything off, match replacement water closely in temperature, and keep aeration steady so the surface stays oxygen-rich. Dim sudden light shocks by switching room lights on before the tank lights where you can, and feed at the surface calmly rather than scattering food that sparks a frenzy.
If a firemouth does get out, and when to worry
A firemouth found on the floor should go straight back into tank water if it is still moist and moving; many survive a short time out, but watch it closely afterward for torn fins, cloudy eyes or fungus on damaged skin, and keep the water especially clean while it recovers. Repeated jumping from several fish at once points away from territory and toward the water itself, so test before assuming behaviour. If a recovered fish stops eating, breathes fast or develops growths on scraped areas, a vet who treats fish or an experienced aquatic shop can advise on what you are seeing. In KinsLe, Care Teams keeps those post-escape observations attached to a named daily check, so the person who finds the lid ajar and the person watching the recovered fish are working from the same timestamped notes.