If you decide to try Firefox again, could you start with "the usual":

If a site is generally known to work in Firefox, these are general suggestions to try when it stops working:

Cache and Cookies: When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes. If you do not see the number going down on the page, you can reload it using Ctrl+r to check progress.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, try either:

• right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button

In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog so you can remove that site's cookies individually.

Then try reloading the page. Does that help?

Testing in Firefox's Safe Mode: In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement? (More info: Diagnose Firefox issues using Troubleshoot Mode)

Also, if you right-click the Back button, is the current page listed multiple times? There are some sites that do that in Firefox, and in past threads it wasn't really clear what caused it. But you usually can use the drop-down to skip over repeats and go back to the "real" previous page.

In "Safe Mode", the problem did go away. It looks like one of my extensions doesn't agree with the new version of Firefox. Adobe Flash & the H264 video are the only Plugins there, so the problem isn't there.

Yes, Safe Mode doesn't disable Plugins, so you can focus your attention on the Extensions list on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then cast a critical eye over the list on the right side. All Mozilla-installed extensions are hidden from this list, so what you see here is your choice (and your responsibility) to manage. If in doubt, disable -- while in regular mode, I don't think this is available in Safe Mode.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

If you have any content blocking extensions then start with those.

Well, fortunately and unfortunately, the continuous loading in Ebay stopped on its own. If it does it again, I'm going through my Extensions. Until then, I was unable to find anything. Ebay's site is full of glitches itself, so I never know what to expect (remember that month and a half when certain pages would load up in HTML only). That was happening in Google Chrome and Internet Explorer also, so don't blame Firefox.