Implement "private" protocol

[Infocatcher]

Allow to use something like private:#https://addons.mozilla.org/ to open links in private tabs.
We should use # to don't encode :...

Related requests:

• Private bookmarks: http://forums.mozillazine.org/viewtopic.php?p=12924011#p12924011
• Open private tab via command line: http://forums.mozillazine.org/viewtopic.php?p=12999125#p12999125

Pro:

• May be used on public computers.
• Allows to open private tabs from command line.
• OK, just because (it seems) I can do it. :D

Con:

• Bookmarks don't looks "private" because they are stored without encryption (but we still don't have last visit date).

---

And bookmarks can be highlighter using following CSS selectors:

.bookmark-item[scheme="private"] {
    /* Styles for bookmark menus and toolbar */
}
treechildren::-moz-tree-cell-text(private) {
    /* Or some other ::-moz-tree-* things, see https://developer.mozilla.org/en-US/docs/XUL/Tutorial/Styling_a_Tree */
    /* Styles for bookmark tree */
}

[Infocatcher]

Test version: private_tab-0.1.4pre6-fx-sm.xpi (source).

[Infocatcher]

Seems like all works fine for me.
But web pages can detect Private Tab now: with enabled private:// protocol such URIs can't be accessed. I'm not sure, bad this or not... but some additional entropy to track user a but better.

Anyway, some other extensions, that use resource:// protocol can be detected too:
http://stackoverflow.com/questions/8548141/can-a-website-know-if-i-am-running-a-userscript#answer-8622744