Whose bugs it is? Firefox 1.5 of Gmail.
Try this:
1. Login into Gmail and wait the page fully loaded.
2. Click on URL drop-down-box and choose a visited URL (other than Gmail).
3. Opps, it goes back to Gmail.
Update: Encounter this problem on other websites as well. Probably a bug in firefox.
(Sometime happens sometime not)
Gmail hijacked our browser!