I learned this afternoon that, in Mozilla Firefox, a bookmark leading to a local directory is actually expanded in bookmark menu itself.
I find this feature very useful especially in handling documentation I store locally. I have, for instance, copies of Roman Catholic documents in a folder. All I have in this particular directory are regular files that are independent of each other, that is, there are no secondary files for these documents in the same directory. If I create a bookmark leading to this directory, the folder will be expended in the bookmark menu, such that I will be able to select a specific document in the bookmark menu itself. Using a keyword that is bound to this folder returns the default directory browser.
Although this feature is very useful in cases like the example above, it does not really help in cases where a directory has too many secondary files. In such cases, the browser just ends up generating a long list of the directory contents for the submenu.