... by changing the 'My Subscriptions' tab that appears on every page into a 'Bookmarks' tab.
That seemed reasonable since I use bookmarks much more frequently than the 'My Subscriptions' page.
I changed the image in a user style sheet (relevant CSS rule shown below) so it loads immediately:
[div class="excerpt" style="margin-left: 1em; border: 1px solid #bfbfbf !important; border-radius: 0.4615em; box-shadow:-1px -1px 3px #999999 inset;"]a#tab-subscriptions img {
[div style="margin-left:2em;"]background-image: url("http://www.democraticunderground.com/imgs/tab-bookmarks-off.gif"
!important;
background-size:140px 26px !important;
height: 0px !important;
padding-top: 26px !important;}
And then changed what it links to with some user javascript (relevant line shown below) which executes when the page is done loading:
[div class="excerpt" style="margin-left: 1em; border: 1px solid #bfbfbf !important; border-radius: 0.4615em; box-shadow:-1px -1px 3px #999999 inset;"]document.getElementById("tab-subscriptions"
.outerHTML='<a href="/?com=myaccount&sub=bookmarks" id="tab-bookmarks2"><img src="imgs/tab-bookmarks-off.gif" alt="My Bookmarks" title="My Bookmarks" border="0" height="26" width="140"></a>';
I should probably do that javascript in a more proper fashion, but it works in FireFox so I'm okay with the quick and dirty approach. Implementation depends on what browser you are using - possibly requiring the modification of the javascript - but that gives you the basic idea...