The shortest, most relevant answer to your question is this:
The short answer is yes, 64-bit operating systems almost always require more RAM than corresponding 32-bit operating systems and 64-bit applications often do require a bit more RAM than corresponding 32-bit applications. There are a number of reasons, but the most basic is that pointers take up twice as much space on a 64-bit operating system as they do on a 32-bit operating system.
I would recommend against trying to 'limit' the resource usage of Firefox in an attempt to lower RAM consumption, as you are likely to greatly hinder its performance, especially when it comes to Quantum multi-processes.
It should also be noted that Google Chrome behaves in a similar manner. There have long been memes and running jokes about how Chrome gobbles up RAM. Firefox Quantum behaves in a similar way to Chrome nowadays because of the degree of separation between the browser process and each individual tab (compartmentalized for stability and security). As a result, add-ons and other things can often be duplicated in each tab process, which is why more tabs = more memory, where this used to have little effect in older Firefox versions.