// Find out whether we're doing line or paragraph selection. If browser.triple_click_selects_paragraph is true, triple-click selects paragraph. Otherwise, triple-click selects line, and quadruple-click selects paragraph (on platforms that support quadruple-click). OO.o support quadruple-click. I'm going to take a look at it.
Looking at GTK2/GDK source code, I found out that it doesn't support quadruple-click. Is it acceptable to do xlib hacks to get it work?
You man GTK2/GDK can't report quadruple clicks? If so, an xlib hack is probably OK.
It seems like it could be a bad idea to go against OS conventions for click count. See http://lists.w3.org/Archives/Public/public-webapi/2006May/0057 (and the testcase in bug 227328) for why.