Edit a gtk-clipboard “in-place”.

edit-html-cb

#!/usr/bin/env python
import gtk
import chardet
import os
import getopt
import subprocess

dtype = 'text/html'
htmlclip = gtk.Clipboard().wait_for_contents(dtype).data
encoding = chardet.detect(htmlclip)['encoding']

# Shove the clipboard to a temporary file
tmpfn = '/tmp/htmlclip_%i' % os.getpid()

with open (tmpfn, 'w') as editfile:
   editfile.write(htmlclip.decode(encoding))

# Manually edit the temporary file
subprocess.call(['vi', tmpfn])

with open (tmpfn, 'r') as editfile:
   htmlclip = editfile.read().encode(encoding)

# Put the modified data back to clipboard
gtk.Clipboard().set_with_data(
      [(dtype,0,0)],
      lambda cb, sd, info, data: sd.set(dtype, 8, htmlclip),
      lambda cb, d: None )
gtk.Clipboard().set_can_store([(dtype,0,0)])
gtk.Clipboard().store()

This is intended a useful hack to make up for Thunderbird's lack of a proper html source editor. Just select all, copy, execute this script (which invokes vi or whatever editor you specify), manipulate, close and paste back into the Thunderbird composition window.