Hello, Please, all bug reports send to my support email so we can discuss it properly. I haven't made any changes there recently so things should work normally - but yes, you need to check the "Disable "Alt" / "CMD" short-keys" option in the Options page / Shot-keys.
Also one more thing... why would "Alt + number" switch between tabs? I thought it's the "Ctrl + number" that switches between tabs in Firefox... maybe it's different in Linux? I will try this in my Ubuntu or install CentoOS.
