Is IE7 in IE8's Developer Tools Compatibility Mode reliable for testing the front-end design of a website?

Question

I've been testing our website on IE 8's IE7 browser mode and it shows some few front-end/misalignment issues here and there. However, I'm not sure if it's completely reliable. I don't want to fix issues that aren't actually being displayed on an actual IE 7 browser.

I need advice whether it's reliable enough to use for cross-browser testing or if we should use an actual IE7 instead.

Thanks.

Answer 1

I can tell you for sure that IE8's IE7 mode is not good enough for testing IE7 compatibility.

It doesn't render accurately as IE7 - I've seen several specific cases where it got it wrong.

It also has quirks and bugs of its own which don't appear in either IE7 or IE8 in normal mode.

We develop our site for IE7 and greater (along with all other browsers of course). We had an incident recently where some of our internal users found they couldn't use the menu on the site.

Turns out that IE8 has an obscure setting which can turn on IE7 mode for intranet sites only. Our users had this flag switch on (without realising it), and so were viewing the site in IE7 mode.

We had tested fully in both IE7 and IE8 and they both worked, but it broke in IE8-in-IE7 mode.

Instead of trying to test using IE7-mode, you should definitely test with a real IE7 install.

I would recommend you install IETester which allows you to run all versions of IE (IE5.5 all the way up to IE9) together in tabs to test your site. It does have bugs and does crash quite often, so it's not suitable for use as a real browser, but it is great for testing.