Thoroughly support this. It could be an elegant solution to an irritating problem.
Due to an update at comparethemarket.com the Website will now not log in whilst in a normal window (clearly their fault as other Websites function without a problem, so they've opted to do something non-standard).
The name/URL of the Website is not something I am going to forget so I don't need to create a bookmark (which I use for less-frequently visited Websites), I simply type in the URL. But, because I only go there a few times a year, I forget and end up going to through their stupid process trying to get me to use a code in an email instead of the password (and the code process is just as flawed,, but more cumbersom because of having to copy+paste the received code (and sometimes to wait for it) so is pointless as well as irritating). Time wasted unnecessarily.
Further, and this is important, if I click on a link in an email from Compare The Market, I don't want the Website opening in a normal window. Both because there may be issues with logging in and because it helps mitigate their privacy invasion (accepting they will know I've clicked the link). Having to copy the URL from the email isn't always easy due to the way some emails get constructed, and is again a burden which it is hopefully easy to mitigate.
It would be far easier to simply enter the URL/click on a link, and have Firefox automatically recognise that it's a troublesome Website and open the session in a Private window.
(Of course, fixing whatever it is in Firefox which is preventing log in would be nice, but it may be harder to identify what the root cause is, compared to creating a gatekeeper list of URLs which must be opened in a Private window?)
Creating a shortcut to open a specific Website in a Private window is cumbersome and whilst it would achieve the desired outcome it is a workaround, not a solution, and it's untidy. I rather like keeping the quantity of icons/shortcuts on my desktop to a minimum (and to what I use frequently), I don't suppose anyone wants to unnecessarily clutter their desktop, or a dedicated folder, with such shortcuts when there is the potential for an elegant solution.
Side notes:
I have systematically disabled all anti-privacy invasion features/add-ons for the Compare The Market website URLs and the only way I can successfully log in is through using a Private window.
I have clicked the Shield and reported a problem with the Compare The Market Website.