This symptom happened when I was browsing Trac and changing tabs at the same time (with alt+1..9). Sometimes the page jumped to a strange link (inside the same page). Turns out that Trac has some access keys and when you hit alt+<number> it jumped to the link with the associated access key. This trick solved it, put about:config on your address bar, and set this option:

accessibility.accesskeycausesactivation = false

Now the link gets focused and the pages are not accessed directly.