Haven't tried it on FireFox 3.6.8. But it does work on 3.6.7. However you can try the following steps as well.

1) First make sure that your Firefox status bar is on view. If not go to View in the menu bar and tick on status bar (Usually the screen grab icon is displayed on status bar)

2) Further you can go to Tools>Add-ons and then select Extension tab from the pop up window. The look for Screengrab entry and Click on Options. There you can configure the image type to be saved.

3) I hope it should work ( check out the screen shot - the right most icon on the status bar)

Dinest I have tried all that you suggest. 1. No icon for screengrab is on status bar. 2. Options under extensions only shows type of image to store PNG or Jpeg.

I have searched everywhere I know how on the menus, status bars and still can not find it., although it shows the add in has been installed.

http://www.screengrab.org/ To use it, just right-click a page to bring up the context menu and look at the options under “Screengrab”.

I have both that Context menu entry for Screengrab and the Statusbar icon for it.

I have updated to firefox 4.0, I wish I hadn't, the screengrab tool bar doesn't show or work , among other things ! and my computer is extremely slow now since upgrading to firefox 4.0 ! It's more trouble than it's worth. I've tried using system restore *failed* At this point I would rather go back to the older version of firefox How do I delete the 4.o ? (so messed-up) How do I get the sceengrab toolbar back? - btw it IS downloaded

I just upgraded to 4.0 too and am very disappointed...no way to find "screen grab" . I hope there is a fix in the works.