When I load that page, all the content below the word "BACK" has been squeezed to the right and I have to use the horizontal scrollbar to see it. Or zoom out (Ctrl-) several times to shrink it.

The reason for this problem, as far as I can tell, is that the BACK bar is floated, and while other browsers do not see a way to squeeze the comparison table into the end of that bar, Firefox does. There are various ways to fix this in Firefox for the page's author, but they aren't convenient for site visitors. So for now, using the horizontal scrollbar is the easiest workaround.

But if you're curious...

For example, the site could add this to its style rules:

.ComparisonTable {
    clear: left;
}

If you wanted to inject that into the page for testing, you could do this:

Select and copy the following script:

document.querySelector(".ComparisonTable").style.clear="left";

Open the web console below the page by pressing Ctrl+Shift+k or using the Developer menu.

Paste the script at the bottom next to the caret (>>) and press Enter to run it. The comparison table should immediately snap into place.

Then you can close the web console by pressing Ctrl+Shift+i or clicking the small x at the upper right of the console toolbar.

Unfortunately, that's a one-time hack and you'd have to do it every time you view a comparison, so hopefully the site will fix it. You might try mentioning it to them; you can link to this discussion.

Note: If you use the Stylish extension or the Greasemonkey extension, either of those could be used to hack that page every time you view it. If you do not already use either those extensions, it may not be worth it unless you plan to do a LOT of battery shopping.