From farther down: "Open visual editor. Click to the right of the either of the 2 tables. Note the bizarre result of the row moving over one cell. Click to the right of a different row and note that row moving over one cell. If you click above or below the table the problem goes away."

See: Wikipedia:Village pump (technical)#Row moving over one cell. Table bug using Flagg template (and others). Or in the archives when it is moved there. See: Template talk:Flagg#Row moving over one cell. Table bug using Flagg template

I am using Firefox on Windows 10 Pro PC. Latest standard versions on both. This does not happen to me on the Edge browser. Whether I am logged in or not. I logged out of Wikipedia and I still have the problem with Firefox. So it is not my JS and CSS files. I also disabled all my Firefox addons and then closed all my Firefox windows. I launched Firefox and I still have the problem with Firefox. No addons and not logged in.

The problem tables all use templates within the table. But it is not a problem with tables using {{flaglist}}.

See List of countries by total health expenditure per capita. Both tables there use {{flagg}}.

Open visual editor. Click to the right of the either of the 2 tables. Note the bizarre result of the row moving over one cell. Click to the right of a different row and note that row moving over one cell. If you click above or below the table the problem goes away.

I opened visual editor for Help:Table and tried clicking to the right of many tables. Closer and farther away. I have noted the problem there with only one table so far. Have to go there to use visual editor on this table:
Help:Table#Table cell templates

I see the problem only with the middle row there. Click to the right of it, and click closer until the row moves over one cell. It doesn't happen all the time.

I removed the templates from a few rows of one of the tables in the list article. This solved the problem. And the small table above only has the bug in the middle row using templates.