Go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) and search for a good ad / pop-up blocker.

Hi EdwardLotz, if this is too long, the main point is the setting under (3)(B), but I want to provide the full background for reference.

As you know, the basic setting is on the Preferences page.

• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Windows: "3-bar" menu button (or Tools menu) > Options
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

Scroll down to the Tabs section and make sure the box is checked for "Open new windows in a new tab instead"

Now... Firefox does make exceptions in some cases:

Dialog Window: Firefox may not be able to open a new tab in certain kinds of pop-up windows. Typically you would recognize these as "dialog" style because most of the toolbar is missing and you do not have a tabs bar. I don't have a workaround for this situation, but these should be rare.

Scripted Popup: If it's a normal window, there may be a script attached to the link. To force scripts to launch new windows in a new tab, you may need to modify a setting. 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
• 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 that help with the problem links?

Now that I re-read your question, I'm not sure whether the popups are opening from a link you are clicking or in some other way. If it's not from a link, then those settings may not help.