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.

Is one of the pages opening in the sidebar?

Opening in the sidebar is the default for bookmarks that are created via a link or button on a website.
You can check the Properties of a bookmark via the right-click context menu in the sidebar (Ctrl+B; Cmd+B on Mac).
In the Bookmarks Manager (Bookmarks > Show All Bookmarks) you can click the More button in the Details pane at the bottom right.
Make sure that "Load this bookmark in the sidebar" is not selected.

You can toggle the Bookmarks sidebar on/off via "View > Sidebars > Bookmarks" or Ctrl+B You can toggle the History sidebar on/off via "View > Sidebars > History" or Ctrl+H

When I opened Internet Explorer to compare, it let me increase the website to a 195 %, which then fills the whole screen of my monitor. Firefox won't let me do this. Peter

Firefox doesn't zoom pages by default to "fit to screen", so you will have to do this manually.

If you have increased the minimum font size then restore the default setting "none" in case the current setting is causing problems.

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

Make sure that you allow websites to choose their fonts.

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

It is better not to increase the minimum font size, but use an extension to set the default page zoom to prevent issues with overlapping text.

You can use an extension to set a default font size and page zoom on web pages.

• Default FullZoom Level: https://addons.mozilla.org/firefox/addon/default-fullzoom-level/

Cor-el, thanks for your prompt help. Problem solved. Regards Peter