|If your old firefox profile folder still exists, search the folder and write down the complete path.|
Then start firefox with parameter -p, to start the profile manager.
In the profile manager, create a new profile, browse to the old profile folder. The profile name can be set to whatever you want. Then click ok and start firefox on it's normal way, without parameter.
If everything is ok, you should have your bookmarks as well, as all your plugins and add-ons.
The path to the profile of firefox is e.g.:
c:\documents and settings\your_username\application data\mozilla\firefox\profiles\abcxyz
where abcxyz is the folder, you have to browse to on creating a new profile.
If the profile already exist, firefox did not create a new one, but uses the existing one.