Browser add-on to download pdfs from specific websites - 2

Need a browser add-on that can download certain pdfs locally once a user has logged in to one of a specified set of websites, and then upload them to another web site for processing. For example: User logs into electric utility account and navigates to a page that contains links to monthly statements in various forms (html, pdf, etc.). The browser add-on will activate once page containing monthly statement links is landed upon. Then user will be able to press a button in browser that will grab and download all available statements to a pre-defined folder on user's computer. User then will be prompted to upload some or all of the downloaded pdfs to another web site. Idea is to capture data locally and then upload to a site for data crunching without revealing login credentials of various accounts to data crunching site. Add-on should be developed in such a way that it can be modified using open-source tools as necessary.