Firefox uses the F11 key to switch between normal view and full screen view. If a website uses that key for its own purposes, I'm not sure whether there is a way to block that.

If a website automatically switches you to full screen, that's annoying, and there's a good chance you can block that. While viewing the page, open the Page Info dialog to the Permissions tab using one of these:

• right-click and choose View Page Info > Permissions
• Alt+t (open the classic Tools menu) > Page Info > Permissions

For "Enter Fullscreen" uncheck the "Use default" checkbox and choose Block.

Does that work?

Is that button hidden or otherwise off screen?

You can check for problems caused by a corrupted localstore.rdf file.

• http://kb.mozillazine.org/Corrupt_localstore.rdf

I think Outlook 365 had an update. When I open Outlook in Explorer, and click reply to a message, the Send, Discard, Insert buttons appear like normal. However, when I click reply in Firefox, the buttons scroll up and aren't visible until I press f11 to see them. It just started doing this.

If you have made changes to Advanced font settings like increasing the minimum/default font size then try the default minimum setting "none" and the default font size 16 in case the current setting is causing problems.

• Tools > Options > Content : Fonts & Colors > Advanced > Minimum Font Size (none)

Make sure that you allow pages to choose their own fonts.

• Tools > Options > Content : Fonts & Colors > Advanced: [X] "Allow pages to choose their own fonts, instead of my selections above"

Can you attach a screenshot?

• http://en.wikipedia.org/wiki/Screenshot
• https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

Use a compressed image type like PNG or JPG to save the screenshot.

I haven't made any changes to any of the screens or tabs. I didn't even realize I could make the font larger! Thanks for the heads up!

Another possible workaround is to force a "repaint" of the screen by switching the zoom level (e.g., Ctrl- then Ctrl+). Other workarounds noted on Microsoft's forums are summarized in this post: https://support.mozilla.org/en-US/que.../972083#answer-482082.