Alternatively there is a Bookmark Keyword extension, that provides a similar functionality.
After installing, add a bookmark to http://askubuntu.com with the title
[as] Ask Ubuntu.
Now it is possible to use the keyword between the square brackets to invoke the bookmark in the address bar. The detailed process is documented on the extension's web page.
As an example, to invoke askubuntu.com you have to type:
(It requires 2 extra key presses, but I think it is a good tradeoff between maintenance and usability. And for an added bonus there are commands that can be appended to keywords to modify the opening process. Eg.:
as:t will open the page on a new tab.)