[Bug 23153] OS X cannot redirect steam:// URL to Steam.exe

https://bugs.winehq.org/show_bug.cgi?id=23153

--- Comment #5 from Ken Thomases  ---
(In reply to tblodt from comment #4)
> This feature can't really be implemented, because only actual mac apps can
> open URLs (or files), and Wine is not a real Mac app.

Correct.  (Where "real Mac app" should be read as "bundled Mac app".)
> You should be able to install the HD pack by running:
>
> wine iexplore
>
> and putting the Steam URL in the address box there.

Even easier would be:

wine start steam://installaddon/halflifehd