There seems to be an issue with FontAwesome in IE8 (maybe also in IE7, I haven´t tried that yet). For me, using FontAwesome, the icons were just displayed as rectangles or vertical lines in IE8. After comparing the @font-face declaration of FontAwesome (https://github.com/FortAwesome/Font-Awesome/blob/master/less/font-awesome.less) and of this gem (https://github.com/seyhunak/twitter-bootstrap-rails/blob/master/vendor/toolkit/fontawesome.less) I recognized the missing format(...) declaration.
I discovered that this was removed in PR #312 but I couldn´t detect why the removal was necessary. Can someone please enlighten me?
At the moment I patched that problem by overriding the fontawesome.less or rather requiring a fontawesome_override.css.less (copied from the FontAwesome repo) which contains the format(...) declaration. Further, I recognized that this workaround also fixes my DeadClient error that I used to have with phantomjs (teampoltergeist/poltergeist#44).
It would help me a lot if anyone could explain why the format(...) declaration was removed in PR #312. Depending on your opinion(s) I will open a PR.
Its caused over confusion of using single quotes or double quotes. We should always use double quotes when using @font-face in CSS.