Mozilla released an update for Window users with Firefox 20.0.1 on April 11th, 2013. This update addresses issues around handling UNC paths. See bug 846848 for more information.
Depending on update settings (Tools > Options… > Advanced > Update Tab), users will be prompted to update within in the next 48-hours. Windows users can also go to Help > About Firefox and click the Check for Updates button. Users may also manually download and install Firefox via getfirefox.com. The next scheduled releases will be Firefox 21.0 and 17.0.6esr on May 14th, 2013.