HOW TO: Prevent websites from disabling new window features in firefox
This article describes how to prevent websites from disabling certain new window features by changing the related Firefox or Mozilla Suite preference setting. Web pages can disable a number of features in new windows opened via JavaScript.
The new window or "popup" may not be resizable and other features such toolbars may be missing, as discussed here. Advanced users can prevent these features from being disabled by editing configuration via the user.js file or in about:config. Prevent websites from disabling new window features - MozillaZine Knowledge Base