Bootstrap 3 - PIECSS to quickly add border-radius to IE6,IE7,IE8 with CSS3 PIE (http://css3pie.com/). Be sure to add it as a conditional stylesheet for IE8 and lower.

Bootstrap 3 - PIE.css

.img-circle{behavior:url(/scripts/PIE.htc)}
.img-rounded{behavior:url(/scripts/PIE.htc)}
.img-thumbnail{behavior:url(/scripts/PIE.htc)}
.table-bordered{behavior:url(/scripts/PIE.htc)}
select,textarea,input,code,pre,kbd,pre{behavior:url(/scripts/PIE.htc)}
.input-group-addon{behavior:url(/scripts/PIE.htc)}
.btn{behavior:url(/scripts/PIE.htc)}
.dropdown-menu{behavior:url(/scripts/PIE.htc)}
.form-control{behavior:url(/scripts/PIE.htc)}
.panel{behavior:url(/scripts/PIE.htc)}
.well{behavior:url(/scripts/PIE.htc)}
.nav-tabs > li > a{behavior:url(/scripts/PIE.htc)}
.nav-pills > li > a{behavior:url(/scripts/PIE.htc)}
.navbar{behavior:url(/scripts/PIE.htc)}
.navbar-nav > li > a{behavior:url(/scripts/PIE.htc)}
.navbar-toggle{behavior:url(/scripts/PIE.htc)}
.navbar-toggle .icon-bar{behavior:url(/scripts/PIE.htc)}
.breadcrumb{behavior:url(/scripts/PIE.htc)}
.pagination{behavior:url(/scripts/PIE.htc)}
.pager li > a,.pager li > span{behavior:url(/scripts/PIE.htc)}
.modal-content{behavior:url(/scripts/PIE.htc)}
.tooltip-inner{behavior:url(/scripts/PIE.htc)}
.popover{behavior:url(/scripts/PIE.htc)}
.popover-title{behavior:url(/scripts/PIE.htc)}
.alert{behavior:url(/scripts/PIE.htc)}
.thumbnail,.img-thumbnail{behavior:url(/scripts/PIE.htc)}
.label{behavior:url(/scripts/PIE.htc)}
.badge{behavior:url(/scripts/PIE.htc)}
.progress{behavior:url(/scripts/PIE.htc)}
.carousel-indicators li{behavior:url(/scripts/PIE.htc)}
.jumbotron{behavior:url(/scripts/PIE.htc)}

Would it not be easier to combine all the selectors and just declare it once?

I have forked your file and combined the selectors. I think this is better.
Here is the link: https://gist.github.com/ElManouche/ba9356819543065a2b68

you can do this as well:
.img-circle, .img-rounded..., .jumbotron { behavior:url(/scripts/PIE.htc) }

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