You can turn off ligatures with the following CSS

-moz-font-feature-settings: "liga=0";

This worked for me, but according to the documentation it's not really a supported feature and may change as the CSS3 specification evolves.

See also https://developer.mozilla.org/en/CSS/-moz-font-feature-settings

Oh well, nice to see there should be a fix, but... Fix doesn't work! I just added the

 -moz-font-feature-settings: "liga=0";

to the text element's style, in the test page, but it has no effect: ligatures still don't show at all.

Can anybody verify that?

You made an error with the order of the rules.

If you use the font property then you set all font properties, so you override the -moz-font-feature-settings in the font rule that follows it.
To avoid such errors, is is always best to define all properties explicitly (font-size, font-family) and not use the generic font version.
It should work if you swap the order.

font: 0.9em MuseoSlab-500,Arial,Helvetica,sans-serif;
-moz-font-feature-settings: "liga=0";

Oh wait, you're right: in a couple of reload of the page something didn't go properly, and the CSS hadn't been reloaded - so I was still using the wrong CSS: too bad that Firebug doesn't show those -moz settings at all, so I was blind testing (...)

--- My original reply: -------------------------------------------------- Well, the theory is clear to me (even though I admit I'm not a web designer/programmer), but unfortunately, even applying the font-feature property after the font one, has no effect. I updated the example, now it has the form you propose - incidentally, that was the first change I tried, and had no luck, hence I tried swapping, though nothing changed either.

You can use {Ctrl + F5} to reload the page from the server, by-passing the cache.

Thanks! Just hoping I'll remember the key assignment ;)

See https://support.mozilla.com/kb/Keyboard+shortcuts