After installing Firefox 5, the overall size of print on the pages is considerably smaller. Need larger print due to eyesight issues.
There are some add-ons that can be used to change the zoom level on all sites, for example Default FullZoom Level - https://addons.mozilla.org/firefox/addon/default-fullzoom-level/
Use NoSquint, perfect add on for this. Adjusts text and zoom separately, global and site specific settings. I haven't found anything that works as well as this, and until it's compatible with FF4 I ain't switching! https://addons.mozilla.org/en-US/firefox/search/?q=nosquint
There is no such thing as Firefox 5. The latest version of Firefox is 4. Therefore, you cannot have installed such a thing as Firefox 5, and you cannot be having a problem with the text size in it.
Under the File menu there is a menu for print format. There you can change the scaling of the printout.
With many printers, you may also be able to change the scaling in the printer settings for the printer driver.