Unicode play icon ▶ present in a page title is incorrectly displayed in my Firefox

Right-pointing triangle Unicode character ▶ (U+25B6), most notably used on YouTube, is vertically squashed on my tabs, title tooltip and in history in my Firefox 24 beta on particular Windows 7 computers (it did not work in FF 22.0 nor 23.0.1 either).

It is displayed correctly on Windows taskbar tabs and inside web pages themselves - compare the play icons in following printscreen (they should look the same):

Funny thing is, it displays correctly on 3 computers I used in Slovakia a few days ago, but incorrectly on 3 computers here in the UK. And no, changing the Region and Language -> Format setting did not help.

I also ran all the Windows updates, changed Windows font size, installed a beta version of Firefox, ran it without addons - nothing helped so far.

I am lost - what Windows/Firefox setting changes the appearance of this character?

EDIT: the problem has been fixed at least since Firefox 34, but probably even in some previous versions.

Disabling Hardware Acceleration fixed the problem for me.

Firefox > Options > Advanced > General tab > uncheck Use hardware acceleration when available in Browsing section

reference: https://support.mozilla.org/en-US/questions/968277