How to click on a link in ThunderBird, link that opens in FireFox, without losing focus on ThunderBird?

My blog posts starts with the following two assumptions:
1. You use Mozilla’s ThunderBird and FireFox as main applications for email and, respectively, opening links; also, my solution is tested on Windows only; but I remember the same problem when working on Linux for a year;
2. You are annoyed that each time you click on an link from an email in ThunderBird, the current application (ThunderBird) loses focus and immediately switches to FireFox;
3. You need to click on a lot of links in ThunderBird, for my solutions to be worth the time spent on them.

So, how to solve the problem?

I have two simple solutions for this problem and they both involve one thing: don’t let FireFox steal focus on its startup. So when starting FireFox, it shouldn’t have focus, and the very first time you let FireFox have focus, my solution magically vanishes.

First of all, make sure FireFox is not running. Then, do the following. These are the two alternative solutions (different options):
1. Open FireFox and very-very fast (or a bit slower if you have time) press Windows + D to show the desktop; alternatively, you can click the “Show Desktop” icon in the tray; if things go well, FireFox should start minimized and without focus;
2. Open FireFox and then again very fast open another application. The new application should have focus, while FireFox launches in background.

Now you can switch to ThunderBird and no matter how many links you click on it, FireFox won’t steal focus (hopefully). Please remember not to switch to FireFox, or you’ll have to repeat the procedure of starting FireFox.

Does this help you?

Update: another solution has been provided by ciccio in the comments: Open Firefox, type about:config, and, with care (you might want to do a back-up first), set browser.tabs.loadDivertedInBackground to True.