So what site is happening at?

TY for your Q, Mark. Actually the prob occurs when I try to open a (local) PDF. I solved the issue by using Win11 to associate Opera with PDFs. That said, I'm disappointed in Mozilla, since I generally have a very high opinion of FF over the alternatives that are supported on Wintel machines (i.e. MS Edge, Opera, and Chrome). This is the first time in many years - or perhaps ever - that I feel disappointed. The issue almost certainly has to do with the limitations of the Asus E410 in terms of screen size (?). That doesn't make me happier. I suspect there's an "x" located in the lower left or some other option about which I'm unaware. But thanks again for your reply.

If your opening local PDF you can use the free Acrobat Reader to open your PDFs.

I tried installing Adobe. Not only is it almost 1GB (talk about bloatware!) but I'm pretty sure it installed McAfee without my consent. I spent an hour trying to get McAfee off my system (they even have a removal tool which doesn't work). I had to go into the registry and then manually delete a bunch of files. (Win11 still "thinks" it's an installed app). McAfee is a MENACE and I don't need it with Windows Defender anyway. (Besides I have my OS backed up and keep all my data files on USB drives). I already have Opera which I use for Gmail, so I can close FireFox and get the cookies cleared automatically whenever I run out of free views on sites like Slate. Opera works just fine for PDFs (even those that are "fillable"). Still, this is the first time I've run into an issue with FIrefox which is far and away my preferred browser for most things. For example, it has great extensions that let me do stuff like D/L videos from Youtube. I also use uBlock which is great for blocking ads.

Adobe and Adobe Reader aren't the same. One is free and the other isn't. One should always "Custom" install to remove unwanted software during the install "NEVER" use express install but verify what is being install and "uncheck" those so you don't get software or installs you don't want. If you have Windows 7 and up Defender is free and works just fine for me. As to your setup no one but yourself knows that setup or the configuration setup to run. uBlock to me is not good I use Adblocker Ultimate and it works just fine.

Point VERY well taken about avoiding the Express install. Silly me. I was in a hurry. That said, my Asus E410s were super cheap ($140 for the first one, $160 for the second, I think they're up to $180 on Amazon now). However they only come with 56G of ECC memory on the SSD (which is the same memory type as in cell phones). Great battery life, extremely lightweight - 2.8 lb.s. My first one works great after almost 3 years and the screen is almost as bright. Which is a long-winded way of saying that I avoid installing anything that I don't really need, even if I could move it to a USB drive. (BTW I have a theory that larger SSDs decrease battery life. Not sure if that's correct.) Anyway Opera is fine for PDFs - I don't care. I've noted your reco for Adblocker Ultimate and will try it if/when uBlock isn't working for me. Thanks for that tip, too. BTW I use "Easy Youtube Downloader Express" and "Youtube Downloader Button by Nostrum as a backup (sometimes the first one doesn't keep up with Youtube).