Thanks - did as you said: leaving factory test mode manually after firmware upload via firefox and applying calibration afterwards.
As Slider&Touch is now accessible option on both updated Gliss units, I think it's fair to say the 2.0 upload can be considered successful!
Thank you for your support!. In hindsight the "work-around process" was solid and easy. Please understand my temporary anxiousness. Since Gliss is a most valuable module for me, I'd have been gutted having it bricked by user error.
Thank you for 2.0! Super valuable upgrade whilst not cluttering up the UI with hundreds of additional features - great effort!
If the firefox-bug only means that one has to do the web-udate twice leaving the module connected and manually exit factory test mode at the end, I think it would be fair to claim that it basically works as well. With help of a little demo-video I think any firefox user could be enabled to do this update. Maybe that would be less hassle than getting the mozilla-crew to finally fix that auto-reconnecting-bug of firefox.
Can't shoot such a video at the moment but if it helps I can report back over at modwiggler that firefox did the job in my case, illustrating the procedure.
Cheers and thanks again!