Ver 65.0 moved my tabs above address bar

Best place to post this kind of request for help is in mozillaZine forums here: http://forums.mozillazine.org/index.php Really the issue you are experiencing has nothing to do with PortableApps implementation of making Firefox portable. Really the issue lies with Firefox itself and hence posting on a forum dedicated to Firefox is the best thing to do - better chance of getting help there.

Some other people are reporting the same problem at mozillaZine with Firefox 65.0. For example, this (there may be others just read down the mozillaZine forums posts): http://forums.mozillazine.org/viewtopic.php?f=38&t=3046550

Seems the CSS code required to achieve tabs on bottom has changed as of FF v65.0

EDIT: If you find CaJazzman a bit confusing then this would seem to be the code you need: https://github.com/MrOtherGuy/firefox-csshacks/blob/master/chrome/Fx65_t...
Seems people are reporting multiple issues with CSS being changed as of FF 65.0. If you get stuck just ask a mozillaZine, they are quite friendly and helpful there.