A few things to check:

(1) Full screen mode

The F11 key switches between normal and full screen modes. Make sure you are in normal mode with all the regular bars showing.

(2) Compatibility

One thing that sometimes happens is that Windows sets up Firefox in a compatibility mode. If the whole desktop changes resolution when you start Firefox, then that is the first thing to check. Close Firefox, right-click the program icon you use the start it up, choose Properties, then the Compatibility tab, and clear out any checkboxes that might be checked there.

(3) Zoom

It is easy to zoom the page accidentally using the mouse scroll wheel. To reset zoom, you can use Ctrl+0 (that's a zero) or

View menu > Zoom > Reset

When you are using the orange Firefox button (short menus), you can tap the Alt key or press F10 to display the classic menu bar to use the old View menu.

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If those don't help, can you describe what sites are affected?

One other thought: sometimes the window is larger than the screen. When you can't see the corner, it is tricky to resize. One approach is as follows:

With the Firefox window active, press Alt+Spacebar to open the control menu, then press s or click Size.

Next, press the right arrow key once, then press the left arrow key repeatedly until the edge of the window comes into view. Press Enter to lock in that position.

Repeat for the bottom of the window: With the Firefox window active, press Alt+Spacebar to open the control menu, then press s or click Size.

Next, press the down arrow key once, then press the up arrow key repeatedly until the edge of the window comes into view. Press Enter to lock in that position.

Firefox should remember that new size. Try to close any badly sized windows before closing the one you fixed.

Thank you for your speedy response... I feel like an idiot now. After I posted this question I was checking for useless add-ons that sometimes get downloaded unnoticed with other progammes and deleted the Babylon toolbar... bingo! all fixed. Sorry to be a pest, but maybe it's something to think about. I'm sure it came with Firefox.

Cheers, John

This issue can be caused by the Babylon Toolbar extension

• https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

Start Firefox in Use Troubleshoot Mode in Firefox to check if one of the extensions or hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

See also:

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

THanks for your suggestions. Much appreciated.