Firefox has a full screen setting that hides the Taskbar even when Autohide is not enabled. Could you check whether that is the problem? The F11 key switches full screen mode on/off. (This is different from the kind of full screen web pages can invoke. Usually you click a button in the page to go to full screen, and tap the Esc key to exit.)

If full screen is not the problem, hmm. Sometimes the settings file that stores window dimensions becomes corrupted with nonsensical values. You can rename the file and have Firefox rebuild it. Here's how:

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > Help > More Troubleshooting Information
• (menu bar) Help > More Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, on the Profile Folder row, click the "Open Folder" button. This should launch a new window listing various files and folders in Windows File Explorer. (For example, there should be a folder named bookmarkbackups at or near the top of the list.)

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > Exit
• (menu bar) File > Exit

Pause while Firefox finishes its cleanup, then:

Right-click xulstore.json then Rename to something like xulstoreOLD.json

Start Firefox back up again. Do windows display normally again?

That mini-reset may hide the bookmarks toolbar and/or menu bar. You can use one of these methods to show the toolbar list and select the desired bars there:

• right-click (on Mac Ctrl+click) a blank spot on the tab bar (or the "+" button)
• (menu bar) View > Toolbars
  On Windows, tap the Alt key or F10 key to activate the menu bar temporarily.
• in Customize mode > Toolbars button (see: Customize Firefox controls, buttons and toolbars)

To turn on the Menu Bar, click it on the list. There are multiple options for the Bookmarks Toolbar.

Thank you! Some messing around with FLock/F11 fixed the issue, although FF exhibited some strange behavior as I toggled between the full screen on and off. With full screen on all my tabs across the top were invisible as was the task bar, where before the tabs were visible but the task bar wasn't. When toggled to full screen off both the tabs and the task bar reappeared. So, I seemed to have been stuck somewhere in the twilight zone in between settings. Also, auto-hide is now working again, so that's good!