when i use FF's web developer tools and change the encoding back to UTF-8 from ISO-8859-1 or Windows-1252, the characters are "gibberish"... this makes no sense because they are displayed properly when initially viewed with this particular setting at UTF-8
Does your html show the "real" characters, or numerical entities? Entities are immune from encoding issues-- but they are otherwise unreadable. Judgement call.
Why are you changing encodings at all? Make sure every page has a charset declaration, or set it globally for the site.
No matter how obscure the character, it's in UTF-8 somewhere. Here it sounds as if you're describing the "box drawing" range, which was incorporated specifically because one longago OS used it.
:: shuffling papers ::
hex 2500 - 257F (decimal 9472 - 9599)
Is the sole purpose of your embedded font to display these characters? If so, let users stick with a local font if they've got one. For me that's
:: further shuffling of papers ::
Hm. Buncha CJK fonts, Apple Symbols, Apple Gothic, Arial Unicode, the usual third-party fonts. Someone will know if there's something in the standard Windows package that covers the same range.
:: detour to refresh memory ::
In @font-face rules, as in other CSS font declaration, list possible sources in order of preference. So first "local", then "url".