TL;DR (From Android Authority)
• Mozilla responded to a review mentioning the lack of tablet UI optimization for Firefox on Android.
• Mozilla confirmed that its team is not working on optimizing the tablet experience at the moment.
• Mozilla did, however, say that it hopes to revisit tablet optimization when time and resources permit.
As a Pixel Fold owner, I agree. I switched to Firefox on desktop, but the bad unfolded interface prevents me from using it on mobile. Luckily I can use extensions with Kiwi, but I’d rather not use a Chromium browser.