I tile within one monitor when I legitimately want to see things side by side, but I certainly don’t want firefox permanently taking up screen space when I really only need to occasionally look at it. Usually it’s on a separate monitor in the same workspace, or in a dedicated workspace.

Maybe there’s some way I could manipulate stacks and zooms to achieve that within one workspace, but I’ve always found it easier to just have firefox on a separate workspace I can easily quickly swap to and from when needed.