@mapx, thank you for the link.
From my personal experience I know that running Iron in single process mode is safe and stable. I run browser exclusively in that mode since middle of 2010. And I have not seen any problems with it related to safety and stability. So, for me explanation, that running browser in multi-process mode is required for safety and stability, is just a myth.
On the other hand - running Iron in multi-process mode (default) is a way more resource consuming experience, comparing to running it in single process mode. And BTW, if you run it in single-process mode, while executing browser's code, CPU doesn't need to switch its context between processes very often, making overall experience that it runs faster. Switching between threads is way faster than switching between processes. That's why multithreading is widely used - it's fast. Additionally, from the security stand point, one should always watch which processes are loaded in memory and executed all the time (or run antivirus programs on the background permanently, that will do the same, but make your computer run slow). I don't need antivirus programs running on the background all the time, because I have brief alert sound associated with event when new process is launched. It's very convenient and allows me to see what's going on. Now, imagine if browsers will start new processes every time I click on a link and open an new tab... And look at Task Manager when you open tens of tabs (it happens quite often with me)...
But again, the main two reasons why I always run Iron in single process mode are: less resource consumption and overall speed.
Now, it's pity to see how deteriorates that mode in the latest build. I found on the Internet post with similar complain here:http://www.dslreports.com/forum/r27188385-
As you see with v19 now one has to choose between ability to login in web sites and to see browser's settings page. It's weird, indeed... This new bug is not present in v18 or any earlier versions of the browser.
I'd really like to see it just start working again... Not everyone wants to buy a new supercomputer just to be able to run a new web browser.