Enough of the browser wars. Use two.
Have you ever needed to sign in at the same site under two different accounts? Imagine multiple tabs opened with multiple application and tasks in them at different states of completion... Signing out is just troublesome. There are special modes like Chrome Incognito, but isn't Firefox with all required extensions and settings better for this?
Not all browsers equally well support and especially implement certain features. The situation when something does not work as expected may be subtle, specific or otherwise weird. Quickly switching to another browser will help more than loyalty.
Some functionality of the browsers comes with extensions. And some extensions are better in specific browser. Accept the imperfect world as is and use each browser for what it does best.
Normal human opens multiple tabs in any browser - this is convenient. The more web-based applications are used, the more it is required to frequently switch between them. Switching tabs within browser is not as visual as switching windows within desktop environment (ALT + TAB). Using two different browsers enhances visual experience as the two windows have different icon.