I could reproduce the bug on my machine on Windows 8.1. What's more important: I could reproduce it even when 7+ Taskbar Tweaker is not running, which means that it's an issue of either the taskbar or Firefox, not of the tweaker.

A further investigation has to be made to understand what causes the issue, and whether only Firefox is affected. Also, you might want to file a bug report to the Firefox team.

Unfortunately, Excel doesn't play well with the taskbar. See my reply here:
http://tweaker.userecho.com/topic/529194-middle-cl...

There's no real fix for the taskbar, Excel is the program that requires fixing.

I will try your settings on a Windows 7 machine when I have the chance.
Meanwhile, please try the following:
Restore the tweaker's thumbnail settings to default (or even better, close it altogether), hover over the Firefox button to show the thumbnail, and wait for a couple of additional seconds. Is a tooltip shown up above the thumbnail?
It should, and the tweaker relies on this behavior. If it doesn't, then it's probably an issue of Windows.

A screenshot of your taskbar and of the tweaker's options will help. Please paste those, and I'll try to reproduce your issue.

Please see my answer here:
http://tweaker.userecho.com/topic/172218-double-cl...

I cannot reproduce this. Note that if the title fits the button, no tooltip is shown.
Could you paste a screenshot?

Excel 2007 has numerous problems with the taskbar, and this is one of them. If the window in inactive, it's brought to the foreground instead of being closed. It works with Windows because Windows brings the window to the foreground before closing it.

I checked it, and could reproduce the issue.
The problem is indeed caused by the InkSaver program. It injects code into the 7+ Taskbar Tweaker process (among others), and hooks the GetProcAddress function, which breaks the injection. I think you should report it as a bug to InkSaver, especially if you're a paying client of theirs.

A duplicate of: http://tweaker.userecho.com/topic/517022-after-the...
This should be fixed in the most recent beta version.