And a side issue, before it started doing this a few hours ago, even with firefox set to load 'blank page' on new tab when starting firefox it loads a 'new tab' instead of fast dial.
You should set Firefox to load 'chrome://fastdial/content/fastdial.html'

I've been forced to disable fastdial because with it installed my address bar is erased, and even if i manually add it back in i can't type anything in it. disable/restart and it works perfectly.

This may be a conflict with another addon. Could you try to install Fast Dial on a new profile (run "firefox -p" from command line and create a new profile) to check this out?
Also could you check Error Console (menu Tools > Web Development > Error Console) for errors?

For my part,
I have a conflict with Adblock addon (publicity blocker).
New tab impossible, opening a new window it works, then I close the first tab

Apologies!

I have an old XP (cracked). And I can not install a newer version Firefox.
This is perhaps why ?.

Adblock Plus must not be compatible with my old version (?).

When I click on the "new tab" button (+) in the tab bar, nothing happens. I open a new window, the problem is resolved.

I can say it...

I am curious

Are you also using by chance the Extension

Adblock Plus Pop-up Addon