Hello lpcornel ,

Follow the instructions and step :

1 Launch Firefox. Click the “View” tab on the program menu and choose “Toolbars.” Select “Customize” from the fly-out menu and a “Customize” toolbar screen loads.

2 Deselect the “Use Small Icons” box and click “Done” to enlarge the icons on the Firefox toolbar.

3 Click the “View” tab and choose “Zoom.” Select “Zoom In” from the fly-out menu to increase the display of Web pages in Firefox. Repeat this step to increase Web page display even further.

4 Click the “Firefox” tab (Tools menu in Windows XP) and choose “Options.” Select the “Content” icon on the “Options” screen. Click the “Advanced…” button in the “Fonts & Colors” section to load the “Fonts” window.

5 Open the “Size” drop-down menu in the “Proportional” field and select a measurement that is greater than the default value. Open the “Size” drop-down menu in the “Monospace” field and select a measurement that is greater than the default value. Open the “Minimum font size” drop-down menu and set the smallest possible measurement for Web page text. Click “OK” to expand the font display on Web pages in Firefox.

I hope resolve your problem then reply me back.

Thank you

This step was not available:

2 Deselect the “Use Small Icons” box and click “Done” to enlarge the icons on the Firefox toolbar.

If you google: firefox "use small icons" there are numerous references that this feature does not work.

That is likely the standard Linux GTK file chooser, so you have to check this in the Linux GTK settings or in the Linux theme settings.

Hello...

I discovered the solution through random clicking around on the FFox file dialog. Apparently the dialog was maximised, just that this is not reflected in the state of the Alt-Space menu in the top-left corner. I happened to right click on the Title Bar of the dialog and voila, a popup menu appeared with Restore enabled, and Move and Resize are disabled! I have no clue why the two dialog popup menus show completely different states, but problem solved.

thank you..

That is likely the standard Linux GTK file chooser, so you have to check this in the Linux GTK settings or in the Linux theme settings.

Changing the firefox boolean in about:config for "allow_platform_file_picker" did not work for both true and false.

Hello... I discovered the solution through random clicking around on the FFox file dialog. Apparently the dialog was maximised, just that this is not reflected in the state of the Alt-Space menu in the top-left corner. I happened to right click on the Title Bar of the dialog and voila, a popup menu appeared with Restore enabled, and Move and Resize are disabled! I have no clue why the two dialog popup menus show completely different states, but problem solved. thank you..

What firefox version, operating system/DE? In my case, Firefox 77.0.1 (64-bit) in Arch Linux with KDE Plasma ver. 5.18.5. What you described does no such thing. In fact this response appears to be totally unrelated to the problem described.