How are you opening the pages?

Are you double-clicking the file in a file manager to open the default browser or via other ways?

Does it also happen when Firefox is already running?

Normally I open local pages I compose myself with Dolphin (Open page in browser icon) but even when I ctrl/O or File/Open File - I get the same results, e.g. an alert message that I must click OK to remove. I have tried: clear history, clear cache, override auto cache management (on/off) w/same result. I'm out of try-dis and try-dats that I can think of. Normally I will already have a browser window open when I try my local pages. These pages are nothing special. I compose them as a sort of organized notes pages that have info and links w/o searching Google again.

You can try Safe mode, and, if it helps, disabling extensions to see if one them causes that.

Disabling all extensions did not do the Trick, but while testing disabled and enable extensions, one at a time I had a local page open that did not show the Alert!

It turns out that every page which prompted the Alert! had a meta tag of: <meta http-equiv="refresh" content="5; URL=http://" <="" p="">

Mark as Solved, and thanks to all who responded,