Updated: May 22, 2013
You are facing the following problem - You are running Windows 7 or higher and your browser of choice is Firefox. Sometimes, you download pictures and documents from various websites, and you like to save them somewhere. To that end, you do the necessary, right-click - save as, and a dialog window pops up. The problem is, it takes several seconds for the contents of some of the selected folder to show up. Every time.
This short tutorial will explain what the problem is, and how you can work around it. You will learn a little about component search, Windows internals, and a few simple tricks besides. And as always, you will learn the art of under-kill, which is the opposite of over-kill, which tells us that you will get suggestions as wild as scanning for malware, reinstalling Windows or purging Firefox. None of that, follow me.
Problem
In more detail, you notice the problem manifests when you try to save your documents to one of the Libraries. For those wondering what Libraries are, they are a new-old sort of addition in Windows 7, replacing the classic shortcuts. You add your desired directories to Libraries, or make new ones, and then they show up in the sidebar of your Windows Explorer. Simple. And sounds rather useful.
Now, here's the funny thing. When you try to save documents into one of these Libraries, the refresh of the contents of the folder takes a long time. And it gets longer the more data there is in the folder. One with say 50 files, it takes a second. One with 1,500 files, the time climbs to three or maybe four seconds. Slow and annoying.
Solution
To debug this kind of problem, you must first ignore all online solutions, but this is kind of a paradox, else you would not be reading this article. But what I'm trying to say is, do not start applying random fixes blindly until you figure out the scope of your problem.
For example, when I faced this issue, I got all kinds of results telling me to delete a certain download history file for Firefox, as it may be slow. Which is bollocks for several reasons. One, most of those articles are dated six or seven years back. Two, they assume the download list is blocking the whole process, which is most likely never the case. Three, they offer irreversible changes, which you should carefully examine before testing.
Then, there's another matter - you clearly remember your Save as dialogs being fast. And this is where the component search comes into play. If you select any one Favorite folder or drive where you keep data, you will notice that saves are fast. So it's not a Firefox problem anymore, it becomes a Windows problem. And if you check with other browsers, you confirm your findings. Hence, you know what the problem is and how to work around it.
It turns out that Windows caches directory entries differently for its various data structures, and shortcuts are significantly different from libraries. It seems that libraries do not have a cache, or it's very small, which explains the repeated times needed to display the contents, as well as the dependency on directory size. I am not sure how this problem can be escalated to Microsoft, if at all, but it's surely interesting.
Bottom line: Save as dialogs in browsers pointing to Windows Explorer Libraries with lots of contents will be slow in displaying the contents possibly because of a caching bug in the Libraries implementation. To work around it, you should navigate directory trees using standard methods, or you should resort to simple shortcuts. End of story.
Conclusion
This seems like a silly guide, but it will surely save you a lot of time tinkering with your browser settings, options, profile, with the registry, deleting and installing and uninstalling things, all in an effort to resolve what seems to be a pure, internal Windows issue. For some reason unknown to me, the Libraries in Windows Explorer are rather slow to display contents of folders with lots of entry. Work around it, use drives, navigate the directory tree, use shortcuts, and Bob's your nephew.
Moreover, you also learn more about problem solving - do not rush, do not blindly apply solutions found online, always compare multiple methods and products. In our case, does the issue manifest only with Firefox, or perhaps Chrome or Internet Explorer, too? Are all save as methods and locations equally fast or slow? Only after you've exhausted all your comparison options should you move to actual tweaking and changing the system. And remember, if it worked once, then you should not doubt your setup.
Honestly, I could not find any one other reference mentioning this problem. Either my boxen are unique, or I am, which I am, but if someone has an idea how this should be escalated to Microsoft, I will gladly do it. It's not fair that I submit some 100 Linux bugs every year, I should be submitting Windows bugs, too. See ya.
Cheers.