Arial 13 seems to work for me best as well.
I'm not sure if it was site change or Firefox update


>I *knew* some fonts could be set somewhere but I couldn't remember where - thanks.
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>For me the default font was blank and size 14. Arial 13 is easier on my eyes.
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>I think the new default might be Calibri, which should be OK but somehow isn't working for me on this site. I just set it to Segoe UI 14, think I'll try that for a while.
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>That helps with the message body but doesn't change most other elements.
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>Update 1: Segoe UI 14 is ugly when bolded for forum names in the upper pane. So far Arial 13 is the best all around compromise for me.
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>Update 2: Setting the font explicitly to Calibri is the same as leaving it blank. Calibri 14 is smaller than Arial 13 and definitely not as clearly rendered in FireFox for me.
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>Update 3: Arial 14 is a bit too big for the messages, and is ugly bolded in the top pane.
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>Update 4: Calibri 15 is not bad for the message body but anything bigger than 14 is ugly bolded.