I just blogged about it recently. Here is the whole blog post: Sitecore Template Manager - fix for the Tab key.
And the solution in shortcut:
Open the \sitecore\shell\Controls\Sitecore.js
file and replace the following:
if (evt.keyCode == 8 && (srcElement.className && srcElement.className.toLowerCase().indexOf("checkbox") >= 0) ||
(srcElement.type && srcElement.type.toLowerCase() == "checkbox")) {
scForm.browser.clearEvent(evt, false, false, 8);
}
with
if (evt.keyCode == 8 && ((srcElement.className && srcElement.className.toLowerCase().indexOf("checkbox") >= 0) ||
(srcElement.type && srcElement.type.toLowerCase() == "checkbox"))) {
scForm.browser.clearEvent(evt, false, false, 8);
}