How can I open the current HTML file in a web browser from MacVim?

To do it just once, you can

:!open %

which will call the shell command open with the path to the current file as argument. I don't use Mac myself, but open seems appropriate to me. If it isn't, replace with whatever program you wish the file be opened with.

Of course you can bind a key, if you'll need it frequently:

:map <silent> <F5> :!open %<CR>

And you may want to

:set nowarn

to suppress warnings about unsaved file changes.

See:

• :help :!
• :help cmdline-special
• :help 'warn'

---

Note that you can get arbitrarily sophisticated with Vim scripting. For example, this function lets you view the current unsaved changes by use of an intermediate file:

function! BrowserPreview()
    if &modified
        let tmpfile = tempname()
        execute "silent write " . tmpfile
        call system("firefox " . shellescape(tmpfile))
        if delete(tmpfile) != 0
            echoerr "could not remove " . tmpfile
        endif
    else
        call system("firefox " . shellescape(expand("%:p")))
    endif
endfunction

map <silent> <F5> :call BrowserPreview()<CR>

(Replace both occurrences of firefox with open if that worked earlier.)