I've been using Firefox 3.6.x and 4.0.x beta side-by-side without problems, using separate profiles and the -no-remote startup option. Until recently, when I installed Minefield. Now '''both''' Minefield and Beta are crashing almost immediately after startup. For a long time, both have been crashing automatically after the startup pages finished loading. Now Minefield seems a tiny bit more stable and only crashes as soon as I interact with it (switching active tab, resize window, load an URL). Another difference I notice is that Minefield (4.0b7pre) no longer checks for plugin compatibility, while Beta (4.0b5) still does this. After this check, Beta gives an error "The operation can not be completed because of an internal failure. A secure network communication has not been cleaned up correctly", while Minefield just starts. All versions work fine in Save mode, even after the "The operation can not be completed" error in Beta... I've also tested with newly created profiles, but did not see anything different there.