I am using version: 57.0.1 (64-bit)

Right click >> Open link in new tab.

That doesn't work with buttons and menus. Normally I would use Ctrl click on links to do that.

I should have been better at describing the issue. It isn't specifically a "Link" that is the issue. They are menu options and action buttons on web sites that use to open in a new tab in the same FF window that now open in a new window.

Try this add-on: https://addons.mozilla.org/en-US/firefox/addon/open-in-new-tab-domain/

Hi AT, the "Open new windows in a new tab instead" should control buttons in websites as well as links. However, if the site specifies features of the new window such as its side or selection of toolbars, then Firefox will allow it to be a window, on the theory that it may be a dialog or something that only makes sense when viewed in front of the page. You can override that to see whether it helps. Here's how:

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

(2) In the search box above the list, type or paste neww and pause while the list is filtered

(3) Adjust the preferences as follows:

(A) browser.link.open_newwindow - for links in Firefox tabs

• 3 = divert new window to a new tab (default) <= This should already be set; if it's not, right-click > Reset to restore the default
• 2 = allow link to open a new window
• 1 = force new window into same tab

(B) browser.link.open_newwindow.restriction - for links in Firefox tabs

• 0 = apply the setting under (A) to ALL new windows (even script windows) <= Try this one
• 2 = apply the setting under (A) to normal windows, but NOT to script windows with features (default)
• 1 = override the setting under (A) and always use new windows

(C) browser.link.open_newwindow.override.external - for links in other programs

• -1 = apply the setting under (A) to external links (default) (this should already be set; if it's not, right-click > Reset to restore the default
• 3 = open external links in a new tab in the last active window <= Try this one
• 2 = open external links in a new window
• 1 = open external links in the last active tab replacing the current page

To return to normal if things go haywire, right-click each "modified" preference and choose Reset.

Does it help with that site?

Thank you jscher2000, that seems to have done it. I tried this on a couple sites where I had noticed the change and it is now working as before.