First of all, I think that the "System.log" and "Console.log" thing went away in Lion.  Launch Console.app and click in the menu: Console ▸ About Console.  I have version 10.7 (377) and it looks like this:



What version do you have?  To use Console, click on "All Messages" in the source list on the left.

Having the 10.6 console on 10.7 indicates that Lion was not installed properly, which means anything is possible.

I don't know what those app cleaner apps do.  When you reinstalled Firefox, did you lose all of your bookmarks, add-ons, and everything?  You should have.  If not, then you still have the same profile and the problem might be in there.

Let me know on the Console version and Firefox profile and we'll go from there.

Hello 'work,

It seems unlikely that BookMacster would be involved in this, especially the part about all of your add-ons becoming disabled.  (BookMacster will quit Firefox during the process of installing its extension.)  But since unlikely things happen in this business every day, I tested it anyhow…

• In Safari preferences, change default browser to Firefox 11.0.
• In Firefox 11.0, enable four Add-Ons in addition to Sheep Systems Firefox Extension 285.
• Relaunch Firefox 11.0.
• Activate Mail.app.
• Click on the link to this thread in my email notification.

Result:

This thread opens in Firefox, as expected.  Firefox does not quit.  Add-Ons Manager shows that the five Add-Ons are still enabled.

* * *

Look in your system Console log and see if there are any interesting messages in there around the last time that this happened.  (For newbies, type "Console" into Spotlight and choose "Console" under "Applications".)  If you don't see anything, type "Firefox" into the "String matching" search field at the top of the Console window.