Above code didn't format well, let's try this:

Adding Object.toString causes $(handler) not to run handler

//// Commenting this line out removes issue
Object.prototype.toString = function() { };

//// Here's the jQuery
// Without this line, ie5 throws exception
// Might be nice to do this on jQuery load failure?
try { $() } catch(e) { $ = false }
// alert(true) not run -- due Object.prototype.toString
if($) $(function() { alert(true) })

jQuery's current browser support is as follows:

• Chrome Current - 1
• Safari 3+
• Firefox 3.6.x, 4.0.x, 5.0.x
• IE 6,7,8,9
• Opera Current - 1

Sorry, maybe I wasn't clear

Object.prototype.toString = function() { }

Causes complete failure of jQuery in Firefox 3.6.17. i.e. no jquery works.

The secondary, more minor issue, is that attempting to load jquery into ie5.5 throws an exception. I've got no problem with jquery not working here. It would just be nice not to get exceptions

Writing to or configuring of Object.prototype is generally considered a bad practice and outside of jQuery's scope.

Also completely stops jquery working in Safari 5.0.5

Also still the same response as above.

Making changes to Object.prototype will cause unexpected behaviour across all UAs and jQuery is not responsible for that.