Step 1
Copy this code:
javascript:function%20sub100(s){return%2 0s.replace('100.','original.');}A='';var%2 0z=open().document;for(i=0;i<document.im ages.length;i++){A=document.images[i].sr c;var%20splits=A.split('/');if(splits[2] =="ic.pics.livejournal.com"){z.write('<a%2 0href="'+sub100(A)+'">'+sub100(A)+'<br>' );}}z.close();
into a new bookmark on your bookmark bar and press it whenever you're viewing an album page in new Scrapbook. It'll open up a new tab filled with links to the fullsize version of all the images on that page of your album (plus the fullsize version of any cover images for the albums that appear on the right-hand side of the screen).
Step 2
And now that you have a page that is filled with links to the full-size images you can use lots of other webtools to quickly download all the images. I recommend using the DownThemAll!! extension for Firefox.