You can move the current tab to the far end with the Ctrl+End shortcut.

• https://support.mozilla.org/kb/Keyboard+shortcuts

You first need to set the focus to the tab bar to make the shortcut work.
You can do that by first setting the focus to the location bar with Ctrl+L or the search bar with Ctrl+K.
Then you can press the Tab key until you see a focus ring on the current tab to indicate that the tab bar has focus.

That doesn't seem to work. I even made sure the tab was selected by clicking on it. Ctrl+End only scrolls to the bottom of the page of that tab.

As I wrote above, that shortcut only works if the tab bar has focus and has a focus ring.
That should happen with Ctrl+K and one press of the Tab key.

Okay, I tried it again. The first time I did follow your instructions exactly, as well as clicking on the active tab. Again, after Ctrl+K, followed by one press of the Tab key, upon pressing Ctrl+End the only action that results is the page scrolling to the bottom. I've tried it several times and on two machines. Same result.

You may need to press the Tab key more than once.
You need to look at the tab bar to see if the currently selected tab get a focus ring.

This is infuriating, is it not? Almost as bad as the fact that any Flash content on any tab immediately disables all shortcuts. Or that FF won't display Sharepoint sites properly.

Anyway, the correct way to get the focus ring on the tab is:

Alt+D, Shift+Tab, Shift+Tab - then you'll see the focus ring appear around the label of the tab. You can then use Ctrl+Home, Ctrl+End, Ctrl+Page Up, and Ctrl+Page Down.

There - now don't ever say I'm not good to you!