I use firefox at work to do my browsing of the interwebz, for some stupid reason i recently ran into a problem where firefox kept asking me for the proxy authentication instead of saving the previous entered information. It would do this for every resource on a page. So when i opened a webpage i would have to click the damn ok button multiple times.
I smal search on google produce the following link : http://forums.mozillazine.org/viewtopic.php?p=3070251
If you don’t want to go reading the forums here is the TLDR solution – change network.negotiate-auth.allow-proxies property in about:config to false
This works for newer versions of firefox too.