It is related to Desktop mode browsing that is now enabled by default for large devices. This can be controlled via a preference under Settings in "Site settings".

Dear TyDraniu, Thanks for your prompt reply. I disabled desktop mode in site settings and it does't change this behaviour. The size remains a third too big of what to expect. Cleaning cookies, history and so on didn't help. I think this behaviour occured after installing this new FF version. Stephan

I have this issue too. I have tried many different things and everything remains the same. Vivaldi does not have this issue and displays website at my tablets native resolution. On firefox everything is zoomed and there is no way to fix it other than going int to accessibility settings and change the font size but that is a horrible solution as you have to try and guess the percentage to reduce it by trial and error.

Overall a terrible experience and much more pleasant experience even using chrome which is sad. seems every time i try to go back to firefox i am reminded of how low of a priority the mobile browser to mozilla. Which blows my mind. the mobile market is plagued the most by ads and firefox is the simplest solution other than a VPN. They should be pushing it to make some money. Guess they have other priorities or getting a payout from some ad company??