Thread:Extension talk:Vector/collapsiblenav does not work on the main page (1.20.2)/reply

Looking at the errors I'd say it isn't just collapsenav, I suspect the search suggestions when typing in the search bar and the table of contents "Show" and "Hide" don't work either.

Based on the errors I'm pretty sure the problem lies in the fact that there is something on your wiki that is unregistering jQuery plugins, thus causing code that is loaded by MediaWiki to be dereferenced. Specifically:
 * module
 * module  method
 * jquery method  (introduced in jQuery 1.4)

See also jQuery, it is important that you do not manually load some (ancient version of) jQuery. MediaWiki ships with jQuery by default. Loading your own causes both incompatibilities (since core uses a a much newer version) and it causes plugins to be dereferenced at run time.