Invalid file hash when installing
Problem: Whenever I try to install FoxTab, it gives me this error: Firefox could not install the file at because: Invalid file hash (possible download corruption) -261
Solution: This error is not directly related to FoxTab. It is general error, and is mentioned in the mozillaZine knowledge base: look for the 'Invalid file hash' section.
There are several suggested ways to fix\workaround that error.
FoxTab shows only single tab
Problem: Why I see only one single tab whenever I open FoxTab?
Solution: If you open multiple windows with only single page\tab in each one of them, you need to make sure that the option Display Tabs of All Windows] is checked, otherwise FoxTab displays only the tabs of the active focused windows.
FoxTab icon is missing
Problem: I installed/updated FoxTab , but I don't see the FoxTab's icon. How do I get start?
Solution: If you don't see the FoxTab's icon in your Toolbar, you can add it manually. Go to:
View -> Toolbar -> Customize.
From the Customize Window you can drag the FoxTab icon back to the toolbar.
However, having the FoxTab icon is not mandatory, you can also launch FoxTab by using your mouse or with keyboard shortcuts.
Can't change the size of FoxTab's panel
Problem: I'm setting the panel size to be small/large/fit-to-browser/full-screen but it remains the same size as it was before I applied the change.
Solution: Pay attention that there are two launching modes of FoxTab:

Flip mode and Interactive mode. Each mode has it's own size setting.
Make sure that you're setting the size of the correct mode.
Can't open FoxTab with CTRL+TAB
Problem: Every time I press CTRL+TAB, FoxTab is opened and immediately closed.
Solution: CTRL+TAB launches FoxTab in Flip mode, you should use it as follow:

Hold the CTRL key pressed down, and repeatedly hit the TAB key.
FoxTab's shortcuts conflict with another add-on
Problem: FoxTab is using the same keyboard and mouse gestures as another add-on which I use.
Solution: You can easily disable or change how FoxTab is launched. Go to the Options window and check for the launching configuration in the Flip mode and Interactive mode panes.