Some websites create their webpages with very small font size which makes it very hard to read the text. Also if you have eye sight problem, then you may not really love to read the small font text. In both of these cases, you may enforce a minimum font size limit on the websites so that they cannot use a font size smaller than the one you have specified. This can be done easily using the No Small Text add-on in Firefox.
You can install the No Small Text add-on from the Mozilla add-ons website. The add-on does not require you to restart the web browser and can be used immediately after the installation. After the installation, you would see a new icon in the Firefox toolbar. Clicking on this icon, you can set the minimum font size limit for all the webpages from the drop-down menu.
By enforcing the font size limit, you set all the web content to be shown with that at-least font size. Some of the websites may not look pretty with this font enforcement. In that case, you can easily turn off the No Small Text add-on by clicking on its icon in the Firefox toolbar. The icon color changes from green to red to show that it is disabled.
So if you are unable to read that small font text material on a website, you can force them to show the text with a larger font size. This is a great option for elder people who usually have eye sight problems.
You can download and install No Small Text add-on from https://addons.mozilla.org/.