I've noticed Firefox (2.0.0.3) occasionally hangs when fetching a
download while another handler is open.  For example, I use xpdf to
view PDFs, and I'll see hangs in opening a new xpdf instance when one
is already about.  This isn't deterministic: it generally works, with
just occasional hiccups.  Such a hiccup can be cured by quitting one of
the xpdf instances (I'm not positive whether it must be the last one
opened).

Attaching ktruss to firefox-bin produces reams of:

  2352      8 firefox-bin gettimeofday(0xb8dfff0c, 0) = 0
  2352      9 firefox-bin _lwp_park(0xb8dfff04, 0, 0x8c73e0c) Err#60 ETIMEDOUT
  2352      9 firefox-bin gettimeofday(0xb8bfff1c, 0) = 0
  2352      8 firefox-bin _lwp_park(0xb8bfff14, 0, 0x8c73f0c) Err#60 ETIMEDOUT
  2352      8 firefox-bin gettimeofday(0xb8dfff0c, 0) = 0
  2352      9 firefox-bin _lwp_park(0xb8dfff04, 0, 0x8c73e0c) Err#60 ETIMEDOUT
  2352      9 firefox-bin gettimeofday(0xb8bfff1c, 0) = 0
  2352      8 firefox-bin _lwp_park(0xb8bfff14, 0, 0x8c73f0c) Err#60 ETIMEDOUT
  2352      8 firefox-bin gettimeofday(0xb8dfff0c, 0) = 0
  2352      9 firefox-bin _lwp_park(0xb8dfff04, 0, 0x8c73e0c) Err#60 ETIMEDOUT
  2352      9 firefox-bin gettimeofday(0xb8bfff1c, 0) = 0
  2352      8 firefox-bin _lwp_park(0xb8bfff14, 0, 0x8c73f0c) Err#60 ETIMEDOUT
  2352      8 firefox-bin gettimeofday(0xb8dfff0c, 0) = 0
  2352      9 firefox-bin _lwp_park(0xb8dfff04, 0, 0x8c73e0c) Err#60 ETIMEDOUT
  2352      9 firefox-bin gettimeofday(0xb8bfff1c, 0) = 0

$ uname -a
NetBSD monolith 4.99.17 NetBSD 4.99.17 (LAPTOP.MPACPI) #0: Fri Apr 13 16:45:57 CST 2007  bsd@monolith:/var/tmp/src/sys/arch/i386/compile/obj/LAPTOP.MPACPI i386

Brian.

-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/
      "Amusement to an observing mind is study." - Benjamin Disraeli