Save Page WE is probably working in both Firefox and Chrome, but saving the file silently.
This may be as a result of a change in Save Page WE 13.7.

Save Page WE 14.0 was released yesterday and the saving should now behave as previously.

To show the 'Save As' dialog box, go to Firefox's Tools > Options, scroll down to the Downloads section, and enable the "Always ask you where to save files" option.