Issues with GridView on IE but not on Firefox

Question

IE takes forever to load my GridView where as Firefox is almost instant (big surprise I know; but you know users and how they love IE).

We have a GridView which when the user scrolls to the bottom loads more entries into the list (basically lazy loading, instead of loading the whole list, it loads 20 entries and when you scroll to the bottom it loads the next 20). However like I said there is a huge difference in how this performs on IE vs FF. When debugging on IE I consistently get Javascript timeout errors.
during this code block:

function Sys$WebForms$PageRequestManager$_endPostBack(error, executor, data) {
        if (this._request === executor.get_webRequest()) {
            this._processingRequest = false;
            this._additionalInput = null;
            this._request = null;
        }
        var handler = this._get_eventHandlerList().getHandler("endRequest");
        var errorHandled = false;
        if (handler) {
            var eventArgs = new Sys.WebForms.EndRequestEventArgs(error, data ? data.dataItems : {}, executor);
            handler(this, eventArgs);
            errorHandled = eventArgs.get_errorHandled();
        }
        if (error && !errorHandled) {
            throw error;
        }
    }

This error AFAIK is the reason we implemented lazy loading (to get rid of the timeouts). However it seems to not be helping, merely duplicating the issue every time is runs. NOTE: prior to our last release it would load all the data as opposed to Lazy Loading.

Also when debugging it seems to cycle on this piece of code when it is "loading" on IE:

Protected Overrides ReadOnly Property ControlSkins() As System.Collections.IDictionary
            Get
                Return Me.__controlSkins
            End Get
        End Property

I believe due to fact that FF displays the data without the timeout that whatever is causing this is specific to IE and maybe common to other implementation of a GridView population.

I should note however that Im not positive that FF communicates with VS like IE does. Meaning that the warnings I get (the screenshot above) might happen on FF and VS doesnt show them to me but like I said FF has no problems with our page.

Followup [similar error q/a]: After further testing the ControlSkins() method that is getting called repeatedly (posted above) here is its value. It alternates between that HybridDictionary and Nothing

I have to continue testing but I think/hope (fingers are crossed) that adding AsyncPostBackTimeout="300" on my ScriptManager (for that widget) has stopped the timeout error. Of course this doesn't help with the large load times on IE.