Open With for Firefox lets you easily open pages in any other browser
Domain name notwithstanding, the add-on feels pretty solid (and has been tested by Mozilla). It adds a set of buttons to Firefox, which let you open the current page in any other browser that you've got installed.
In terms of UI, it's very flexible; you can add entries to the View menu, the main context menu, the main context menu for links, the tab context menu, or the tab bar (like in the screenshot).
Interestingly, on my own system, it wouldn't add Chrome to the list by default (even though I have two Chrome versions installed – Canary and the Dev build). However, it did add Microsoft Pivot, which I had completely forgotten about.
You can manually add browsers to the list, but you can't remove them -- which is a downer. It means I'm stuck with a Microsoft Pivot entry on my list, and that is enough to make me remove this add-on. That's too bad, because this is actually something I need; I often open the current page in other browsers.
Still, if you don't have an experimental browser that you never use this can be a nice solution. It would be even better, though, if the developer added a feature to allow for the removal of browsers.