AdiIRC

"Use Default" checkbox << can be interpreted as "Use as Default" in a quick look, I feel a more appropriated word would be "Restore defaults". Better yet, if I were building that GUI, I would put a Restore button bellow "Font weight" box with live action (restore visible form to default values).

I disagree, there is 2 checkboxes, the boxes are there for a reason.

The titlebar could be more contextual, in other words, if you are editing Menubar (eg. from right click menu), then display something like "Choose font - menubar".

I added that for next beta.

The Sample box could be somehow editable by the user, good to check if the font supports some specific Unicode char (may be waste of time though, since Buffer area uses another font rendering).

I think the sample box does what it's suppose to do, give a quick look of what the font looks like, typically a user changes a font only once during the lifetime of AdiIRC.

Since now you can detect programmatically when form options changed (confirm?!), then make Apply button disabled until some change is done.

Since that cannot be done everywhere atm, it would be inconsistent, so not adding it.