It looks like the Cliqz browser might have been based on an earlier version of Firefox, based on their https://cliqz.com/en/desktop/cliqz-migration page.

Could you try the export steps in the section "Step 2.1 (Optional) – Use Only Cliqz Bookmarks in Another Browser" on that page to create a bookmarks.html file?

(Actually, you can call it cliqzfaves.html or whatever.html, but do use a .html extension as that will make the next step easier.)

Then to import those bookmarks into Firefox, see:

Import Bookmarks from an HTML file

After importing, you may find them all in a new folder at the bottom of the Bookmarks Menu category there in the Library window. If so, you can drag them to their proper folders now to finish the job.

• Bookmarks in Firefox
• Use bookmark folders to organize your bookmarks

Success?

To jscher2000:

   Thank you for suggestion. I have gone to All Bookmarks in Cliqz and followed instructions in Step 2.1. When Show All Bookmarks is opened no bookmarks are displayed, though all of my bookmarks are shown on left hand side of my monitor and can be opened. Thus, I can't proceed to next step of Exporting Bookmarks to HTML and saving the HTML file. Can't determine why all of my bookmarks are not showing up when using Show All Bookmarks—a mystery! I will keep trying to get all of my bookmarks to appear so I can export them and save the HTML file. I think this procedure may be the correct path, just have to get bookmarks to appear.
  Best Regards
  Sternhagen

I would assume that you can use either places.sqlite or backups in the bookmarkbackups folder in the Cliqz profile folder in "~/Library/Application Support/CLIQZ/Profiles" to restore the Cliqz bookmarks in Firefox. Firefox keeps its profiles in "~/Library/Application Support/Firefox/Profiles" (~/Library is hidden). You will have to create a bookmarks HTML backup beforehand to be able to import your current bookmarks once you have restored your Cliqz bookmarks.

See also:

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

I have gone to All Bookmarks in Cliqz and followed instructions in Step 2.1. When Show All Bookmarks is opened no bookmarks are displayed, though all of my bookmarks are shown on left hand side of my monitor and can be opened.

Normally "Show All Bookmarks" defaults to showing the contents of the Other Bookmarks category. Maybe you are a more organized person and have saved bookmarks only to the Bookmarks Menu and Bookmarks Toolbar categories? Click a category in the left column to view its contents on the right side.

To jscher2000: Thank you for suggestion which I implemented. Was able to create HTML file and save with unique ‘Cliqz Bookmarks’ name. Then imported Cliqz Bookmarks file into Firefox after first backing up old Firefox bookmarks as Json file. So my Cliqz bookmarks are in Firefox which is good. But, I found the import process does not retain the Cliqz Bookmarks file name and duplicates the old file header name used years back when I imported bookmarks from Internet Explorer into Firefox. In this situation I recognize there will be a tedious process of reorganizing the bookmarks in Firefox and eliminating duplicates, but my large Cliqz collection of bookmarks have been captured by Firefox. I appreciate your help in this situation and hope your guidance and my experience will help others. Best Regards Sternhagen