> Switching constantly between Emacs and Firefox (e.g., by making Emacs
> open links via a separate Firefox application) is inefficient.
>
> When you say "switching", what does that refer to?
> Are you talking about a UI-level operation?
Yes.
> In what sense is it inefficient?
In the same sense that it's less efficient to perform shell operations
in a separate xterm, rather than doing M-! or M-x grep or M-x gdb etc.
For instance, it's more cumbersome to arrange to view the browser
display and side by side with Emacs, since the browser isn't constrained
to an Emacs window.