Being Apple-built software, Safari/Webkit will always take advantage of all the hardware accelerated graphics capabilities and optimisations available in Mac laptops.
Firefox/Gecko has an excellent rendering engine but Mozilla has often been late to the party with hardware acceleration on Mac.
It's also worth noting that Safari doesn't necessarily support all the same video codecs as Firefox, so for example Zoom might be using hardware accelerated h264 in Safari whereas in Firefox might use a more advanced codec (e.g. VP9) for which your MacBook might have no hardware acceleration capability. If this is the case, Firefox ought to give users the option to disable support for these non-accelerated codecs when running on battery power.
Firefox/Gecko has an excellent rendering engine but Mozilla has often been late to the party with hardware acceleration on Mac.
It's also worth noting that Safari doesn't necessarily support all the same video codecs as Firefox, so for example Zoom might be using hardware accelerated h264 in Safari whereas in Firefox might use a more advanced codec (e.g. VP9) for which your MacBook might have no hardware acceleration capability. If this is the case, Firefox ought to give users the option to disable support for these non-accelerated codecs when running on battery power.