Reset the page zoom on pages that cause problems: View > Zoom > Reset (Ctrl+0 (zero); Cmd+0 on Mac)

• http://kb.mozillazine.org/Zoom_text_of_web_pages

If you increased the minimum font size then try the default setting 'none' as a high value can cause issues like you described.

• Tools > Options > Content : Fonts & Colors > Advanced > Minimum Font Size (none)
• Tools > Options > Content : Fonts & Colors > Advanced > [X] "Allow pages to choose their own fonts, instead of my selections above"

If you need to increase (or decrease) the font size on websites then look at the NoSquint or Default FullZoom Level extension.

• Default FullZoom Level - https://addons.mozilla.org/firefox/addon/6965
• NoSquint - https://addons.mozilla.org/firefox/addon/2592

Thanks for your help.

OK.

On this very webpage, I can see everything on the screen. When I open my bookmarks, on the left of the screen, the screen does not compress, but rather moves the screen image to the right the width of my bookmark menu, and a scroll bar appears on the bottom.

This didn't used to happen.

<view><zoom><reset> has no effect.

I do have a default font type and size set, but my "Minimum Font Size" IS set to "none," and the "Allow pages to choose their own fonts . . ." IS checked.

Before I use an add-on, I thought I should add this additional clarification. This must be something FireFox can handle.

Firefox doesn't resize the browser window if you open the Bookmarks or History in the sidebar.
You would have to zoom out (Ctrl -) to make the page fit if you get a scroll bar in that case.

Thank you