My first thought was cache and cookies.

My second thought was extensions because you have two FB-specific ad blockers as well as some other "content altering" extensions. But you already checked that. How did you test that: did you restart in Firefox Safe Mode?

Are you using a very high zoom level? Firefox shows a little oval toward the right end of the address bar if the site has been zoomed. You can click that to reset to 100%, or hold down the Ctrl key and tap + and - to try different levels.

didn't try safe mode ... will do that and see what happens. zoom level is good. Only page that doesn't work is the news page... all other pages work fine.

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)

Can you attach a screenshot?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot

A bookmark that opens in the sidebar is the default for bookmarks that are created via a link or button on a website. You can check the properties of a bookmark via the right-click context menu in the sidebar (Ctrl+B; Command+B on Mac). In the Bookmarks Manager (Bookmarks -> Show All Bookmarks) you can click the More button in the Detail pane at the bottom right. Make sure "Load this bookmark in the sidebar" is not selected.

safe mode - loaded correctly ... gonna go through add-ons and see what the culprit is. thanx

not a bookmark problem ... works on all pages except news feed. also works in chrome

found the extension that was interferring ... a social adblocker. Of course it was at the end of the list, but at least facebook loads correctly again. thanks for your help

Awesome. If you liked that extension, you could check for updates and/or report the problem to its author. But if it wasn't helping that much, maybe it's not important.