Awesome. Support forum truncated my description.

Full description: Company runs Atlassian Confluence 2.9.2 and Atlassian Jira Enterprise Edition, Version: 3.12.1-#299. Firefox 3.6.3 works fine with them; Firefox 3.6.4 and 3.6.6 cause the login page to hang (blank page, no content, spinner keeps spinning). Behavior is the same with a pristine profile (used Profile Manager to create a new profile, then start with that profile and immediately access Confluence or Jira).

See also:

http://forums.atlassian.com/thread.jspa?threadID=45680 http://forums.atlassian.com/thread.jspa?threadID=45679

So I've finally discovered the problem.

Upgrading from Firefox 3.6.3 to Firefox >= 3.6.4 reset my proxy settings to "Use system proxy", when it was "no proxy".

The system proxy and proxy exceptions are reset by group policy every 20 minutes (no, really), which is one reason why I'm using Firefox to begin with.

Setting my proxy back to "no proxy" causes things to work properly now.

Kind of miffed that Firefox reset my proxy settings without telling me....