Yes, you can backup your bookmarks (and other settings) before doing a re-install. Please see the instructions in this article: Back up and restore information in Firefox profiles.

To be on the safe side, it is better to backup your bookmarks etc. But note that you can uninstall Firefox without losing your bookmarks. While uninstalling, do not select Remove my Firefox personal data option. For more details, see this article: Uninstall Firefox from your computer.

thanks for the links but it doesnt work, cause i cant the described path to optain the profile data.

i have only one mozilla folder, called \mozillafirefox\..., not \mozilla\firefox\... how its decribed in the instructions you linked

in this folder there i no folder called profiles so i dont know which data i need. i also tried to find the profile with the search option but didnt find anything.

so, im kinda stuck here

So, you mean to say that following the steps in this section of the article does not show your Profile folder?

Your Profile folder is usually under a hidden folder. That could be one reason why you are not able to find it. Please change your windows settings to show hidden files and folders (see here for instructions: http://windows.microsoft.com/en-US/windows7/Show-hidden-files).

After changing that setting, search for your Profiles folder as described in the article I linked to earlier. If you can still not find it, search for places.sqlite in your entire hard drive (C:, D: etc). If you can find this file, copy it to a safe location. This file contains your bookmarks and history items.

Let us know how it works for you.

thank you very much for your help.

i found the sqlite file and shortly after also the full profile folder. thanks for the tipp with the hidden folders, didnt think of that.

my path to the profile folder was kinda different from the default one, but now i have my backup files with my ~400 bookmarks. (the reason i really wanted this data)

thanks for your help

You're welcome !
As I had mentioned in my first post, if you uninstall Firefox, do not select the Remove my Firefox personal data option and Firefox will not delete your Profile folder during the uninstall process. That way, when you install Firefox again, all your bookmarks etc would automatically be available in the new Firefox. This backup of sqlite file was just to be on the safe side.

In future, you can make your bookmarks safe from such loss by using some add-ons. For example Xmarks keeps a backup of your bookmarks on their server. So, even if you accidentally lose them from your machine, you can always restore them. Another advantage is that you can access your bookmarks from multiple machines (like home and work computers). Another add-on which stores your bookmarks on the web is Delicious.