I guess you're talking about printing?

Yes, the Page Setup previously allowed me to print with different font size. But, now not so.

It works here in W10/TB 52.5. Do you get the same result in safe mode (hold Shift when you launch TB)?

Same exact thing happens in safe mode. Wonder if one of you other folks can check this out, since the upgrade? i.e. File, Page Setup, Scale. To see if your inserting a scale disappears also. Maybe it is a design intention for 52.0? I thought 52.0 was the latest upgrade? Evidently there is a 52.5. How do I get that? I'm running Windows 10.

I have no issues with the daily build I use, check that Thunderbird is actually using the printer you think it is. if the printer does not support scaling I could see this not functioning.

using File > print your print dialog should actually name the printer being used. In my case it defaults to a PDF printer driver and I have to select the correct printer from the drop down list.

I'm using the same printer I used prior to this "today's" update to 52.0. It has been scaling before, just fine. Only since the update was installed "today" have I not been able to adjust font size via the Scale. Thanks for the suggestions. My wife will just have to use a magnifying glass to read the e-mail.

It varies between systems. Here in Linux, the scaling option is on Print Preview and not Page Setup. That makes perfect sense to me; I want to see a preview in order to judge the effect of scaling.

But to cut to the chase, here in TB 52.5.0 scaling still works.