how to force an update with firefox 38 With the old firefox, one could force an update by clicking 'firefox' on the menu bar and then 'About firefox' etc. However, with the new firefox 38 this menu only contains the single entry 'Quit' -- there is no 'About firefox' or anything else.

So how can I force an update of firefox? (OS X 10.9.5).

When I go to firefox->menu->preferences->advanced->update->show update history, it says that 38.0.1 was successfully installed, but that 38.0.5 is 'pending'. How can I advance that state from 'pending' to 'successfully installed'?
There is something wrong with your FireFox.

On MBA 10.9.5 with FF 38.01 there is About FireFox, that also shows new versions available.

Right now it is showing a 38.05 as new version that can be downloaded by clicking on it.

If that for some reason does not work for you you can manually update choosing your language first.

Check your settings for FF updates: