Fix a bug where input would some times be captured by the addon even though an element with the contentEditable attribute had focus.

Fix a bug where the addon would sometimes capture key events even when an element with the contenteditable attribute set had focus.

Bumped supported Firefox version to 4.0b6.
Added SeaMonkey support.

Bugfix for an edge-case at facebook.com.
Previously, when writing a 1 or 2 into the input element for the wall at facebook, skts would 'steal' the event, causing a tab switch. This should no longer happen, and the wall input element should now work like it should.

Minor rewrite of parts of the add-on, the code should be a bit cleaner now.
Tested on Firefox 3.6 Beta 2, appeared to work fine, so I bumped maxVersion to 3.6.*.