Your browser may limit the number of pages that can be opened at one time, or you may have a pop-up blocker enabled. Try holding down the Ctrl key (Command key for Mac) when you press the Open All button. Hopefully that will help.
No? Try this:
You may need to turn off your pop-up blocker for URLOpener. Here is how for several popular browsers:
For Internet Explorer. Click on the Tools menu and roll the cursor over the Pop-up Blocker option, then click on Pop-up Blocker Settings. Type 10bestseo.com/url-opener/ in the "Address of website to allow" field and press the "Add" button, then press "Close".
For Firefox click the Firefox button in the upper left and then roll over Options and then click the next Options. Then click Content and next to "Block pop-up windows" click the Exceptions button. Add "urlopener.com" and click Close at the bottom of the dialog box. Then click OK in the Options box.
For Chrome, when it fails to open your URLs, a small pop-up notice icon ( ) appears at the right end of the search/URL bar ("omnibox") at the top of the window. Click that icon, select, "Always allow popups from https://www.10bestseo.com/url-opener/" then click "Done."
Or, click the Chrome menu in the upper right (the three bars) then click Settings and then Show advanced settings... (at the bottom of the page). Under the "Privacy" heading, click the Content settings button. Scroll down to the "Pop-ups" section and click Manage exceptions. In the blank field under "Hostname pattern," add https://www.10bestseo.com/url-opener/, then in the corresponding field under "Behavior" select "Allow". Then click "Done".
Also, you may STILL need to hold down the Ctrl key or the Cmd key to prevent some of the websites from opening as separate windows.