hello,

you can try command+ctrl+J

Nope. Still stuck in full screen.

Try to rename (or delete) the xulstore.json file in the Firefox profile folder.

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Nope. Still stuck :(

Can you confirm that you see the Bookmarks Manager (Library)?

Make sure that you do not run Firefox in Full Screen mode (press F11 or Fn + F11 to toggle; Mac: Command+Shift+F).

• https://support.mozilla.org/kb/how-to-use-full-screen

Does the bookmarks sidebar work normally?

• View > Sidebars > Bookmarks

Start Firefox in Safe Mode to check if one of the extensions (Firefox menu button/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox menu button/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Problem still there. All extensions disabled. No default theme to disable. Bookmarks sidebar works normally. I do not run Firefox in full screen mode. I’m not sure what you mean with if I can see the Bookmarks Manager (Library). I only have “show all bookmarks” and once I hit that, it opens and all my bookmarks appear and I can edit them. I do not have a specific button/folder called “Library” or “Bookmarks Manager” Once all bookmarks window is open, I don’t even see the red, green and yellow buttons on the upper left corner to close, minimize etc the window. No menu bar - neither Firefox nor apple. I can zoom to mission control and put other open apps in the front and work with them but the “show all bookmarks” window stays open in the back.

Knock, knock. Did you forget about me or is this problem not severe enough?

I'm having this issue too - glad it's not just me - thought I was going mad or just very stupid.

Would love to see a resolution to this...

Thanks for leaving a reply! I found another user (skx0221) posting about this shortly after I did (link: https://support.mozilla.org/en-US/questions/1089478?fpa=1). Maybe removing the xulstore.json file works for you. It did not for me bc show all history/bookmarks window is still stuck in full screen after I installed El Capitan on a new hard drive without adding any other files or software other than mozilla. If you find a solution, could you leave a reply here? I'll do the same. Thanks!

You should be able to close the about:preferences window via Command+W.

In a lot of cases deleting xulstore.json has been reported to recover. Make sure that you have closed the Firefox application before deleting the file. Closing open windows isn't sufficient, so make sure to use "File > Quit" to close the menu bar.

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

As a temporary workaround, you could paste this internal address for the Library dialog into the address bar and press Return to load it in the current tab:

chrome://browser/content/places/places.xul

You can bookmark that, then launch it in a new tab or window as follows:

• New tab: Cmd+Shift+click the bookmark
• New background tab: Cmd+click the bookmark
• New window: Shift+click the bookmark

Hopefully the new tab/window will be "normal sized"

cor-el, can't believe it, after trying it over and over again, deleting xulstore.json finally worked! Thank you!

Thank You cor-el - worked beautifully first time!!

Thank you. Found xulstore and deleted it and problem solved. Item recurred, but no longer a problem.