One note first: maybe it's really what you want, but you should know that there is a difference between
D:\Program Files\Firefox\profiles\profile1\*
and
D:\Program Files\Firefox\profiles\profile1\*.*
- the second one requires the dot to be present in the path, so e.g. the file
D:\Program Files\Firefox\profiles\profile1\Cache\file_without_extension
is not matched (and not excluded) using such mask.
I'm afraid there's no way to exclude one folder only, without its subfolders - sorry.
Now, a few things about the exclusions in general: it's not really needed, and actually not a good thing to do, to exclude every little file you think is safe from scanning.
Scanning of a file is not that slow (I somehow doubt your bookmark has tens of megabytes). The resident protection (Standard Shield) implements some optimization techniques - it doesn't scan the whole file, but only the needed parts - so the file size may actually be irrelevant; it caches the previous result so if the file wasn't changed between two accesses/scans, it's actually not scanned again, etc.
(Well, I think that HTML and similar files are not scanned by default on reading, but rather on writing, so unless you changed the settings manually, you don't have to be worried about reading at all, and I'd say writing is not such a common operation here.)
So, the list of exclusions is meant for cases like:
1. You want to prevent a false alarm until it's fixed
2. You have a folder with known malware files and don't want to get rid of them
3. You want to exclude significant areas (such as a folder with gigabytes of movies, MP3, etc.) - even though this option mainly concerns the on-demand scanner, not Standard Shield
4. You want to prevent a specific conflict with a software that e.g. does some heavy writing into a log file, resulting in the Standard Shield rescanning the file again and again.
So, the list of exclusions is not meant to exclude a huge number of single files. First, as I said, it shouldn't be really needed, and second, the implementation is not really optimized for such a case. Every accessed file must be checked against each entry in the list of exclusions, so a huge list may actually result in a slowdown of the whole system. OK, it will probably be unnoticeable, but still... I advice against it.
