Rated 5 out of 5 stars
The tab displaces a pixel vertically when you enable any Glass with tab variations option with the Australis theme.This review is for a previous version of the add-on (188.8.131.52-signed). This user has other reviews of this add-on.
Hi, take a look at the latest v1.1.2pre1 (-> versions page)
I also added three experimental tab variations for Australis themes, so tabs can get a glassy (non-curved) appearance. This should work with Australis and Australis redesigned 3 Alpha. Maybe it will work too once curved tabs enter default FF builds like already happened on Thunderbird nightlys.
Btw. why using GMF and Australis at once? GMF is indeed an extension but mainly acts like a theme.