Looking up Ubuntu bugs using the bug number can be made easy in Firefox using the following bookmark hack:
In FireFox, select the Bookmarks menu (Alt-B for English users) and then right click on the menu and select "New Bookmark...". Next, fill in the New Bookmark dialogue box as follows:
Now you can just enter into the Navigation bar "bug X" where X is the number of the bug you want to lookup and FireFox will expand to the full URL and load the page.
Kudos to Leann Ogasawara for showing me this trick.