Phorge does not support these browser versions anymore.

Quoting https://css-tricks.com/almanac/properties/z/zoom/: "Many of the rendering bugs in both IE6 and IE7 could be fixed using zoom. [...] Setting zoom: 1 turned on an internal property called hasLayout, which fixed the problem."
See also https://web.archive.org/web/20150906195720/https://developer.mozilla.org/en-US/docs/Web/CSS/zoom

And while zoom is recently seeing standardization per https://developer.mozilla.org/en-US/docs/Web/CSS/zoom there still wouldn't be an underscore prefix character.

Walk up to the library and dive into some dusty books about the wild early days of CSS.

Also, enjoy the conversation about that line using git blame:

https://we.phorge.it/source/phorge/browse/master/webroot/rsrc/css/aphront/typeahead.css;0aa67025f25d30162309d59b4cbe133b6180b2d7$7 - 2011

https://we.phorge.it/source/phorge/browse/master/webroot/rsrc/css/aphront/typeahead.css;7a9d5f8f2de5e44f4014116a47de4ea870361732$7 - 2013

https://we.phorge.it/source/phorge/browse/master/webroot/rsrc/css/aphront/typeahead.css;3cf6f746f0555b4d73d587972d896de99667fb06$7 - 2014

https://we.phorge.it/source/phorge/browse/master/webroot/rsrc/css/aphront/typeahead.css;7aee92b5e95cfc11059e9ff8788e5e53dc88e84d$7 - 2017