Hi, there is a hidden setting for this:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste inback and pause while the list is filtered -- Firefox should list several preferences containing "inBackground"

(3) Double-click the browser.search.context.loadInBackground preference to switch the value from false to true

In case you're curious what "Diverted" refers to in the "browser.tabs.loadDivertedInBackground" preference, this is when a link is targeted to a new window and Firefox sends it to a new tab instead.

I had to google the answer which was 6 years old (2019) to disable FF switching to new tabs immediately (browser.tabs.loadDivertedInBackground = true). Just found it and it currently works for me, but why do people have to search for the answer instead of making it default behaviour? Whats the point of the tab option to switch to new tab immediately if it is left unchecked? I can understand this being a recent issue but its been years annoying people who have to do a web search to find this answer. Thanks.

I had to google the answer which was 6 years old (2019) to disable FF switching to new tabs immediately (browser.tabs.loadDivertedInBackground = true). Just found it and it currently works for me, but why do people have to search for the answer instead of making it default behaviour? Whats the point of the tab option to switch to new tab immediately if it is left unchecked? I can understand this being a recent issue but its been years annoying people who have to do a web search to find this answer. Thanks.

A "diverted" window is one that the site targeted to a new window but Firefox opened in a new tab instead. The purpose of switching to that tab was to accommodate pop-up dialogs that were meant to have an action in the page itself.

This scenario is rare in modern web design, so perhaps the default value should be switched and if it breaks someone's workflow with a specific website, they can toggle it back to true. Or perhaps it should only apply to pages on the same domain so that there are fewer nonsensical instances of switching tabs when it's a different site.

Either change is above my pay grade, but you could request it on Mozilla's Connect feedback site. Search for an existing thread to vote up or use the "Ideas" section of the site (at https://connect.mozilla.org/t5/ideas/idb-p/ideas) to post a new one.