I had some trouble getting your script to run on Firefox / Greasemonkey.  It turns out that I needed to replace this line:

<!-- language: lang-js -->

    // @require http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js

with:

<!-- language: lang-js -->

    // @require https://ajax.googleapis.com/ajax/libs/jquery/1.8/jquery.min.js
    // @require https://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js

With this change, the script seems to work on Firefox (although I haven't properly tested all the features yet).

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I also noticed a few issues with the options pop-up:

* The pop-up appears in a weird location, partially off the screen.  I managed to fix this issue by changing the `style` attribute from the original

    <!-- language: lang-css -->

        display:inline-block; position:fixed; margin:auto; top:50%;
        margin:-100px 0 0 -150px; z-index:2; background-color:gray;
        color:white; -webkit-border-radius: 15px; -moz-border-radius: 15px;
        border-radius: 15px;

    to:

    <!-- language: lang-css -->

        display:inline-block; position:fixed; top:10px; left:50%; width:500px;
        margin-left:-250px; z-index:2; background-color:gray; color:white;
        padding: 10px; border-radius: 15px;

* Having the checkboxes at the end of the option descriptions is somewhat ugly awkward; they'd look nicer and be easier to click if they were at the beginning.  You could also simplify the HTML by nesting the checkboxes inside their labels, as in:

    <!-- language: lang-html -->

        <label><input type=checkbox id=id checked> Text </label><br>

* Every time I open the settings, all the checkboxes get checked.  It would be much better to have them retain their previous state.

* I don't see any particular reason why I *shouldn't* be able to disable all the features, if I want.  That extra check seems just plain useless to me.

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Also, the "add features" link injection doesn't seem to work on the fancy new user profile currently in testing on [meta.SE](http://meta.stackexchange.com). You might want to add compatibility for that, especially since it'll likely be rolled out network-wide sooner or later.