Please advise how I can make the text larger in Firefox.
See Zoom. This will allow you to adjust the text zoom level per website. If you want to change the default text zoom level for all websites you visit, have a look at the
CTRL + 0 is to Reset Zoom
CTRL + + for Zoom In
CTRL + - for Zoom Out
You can also try the Default FullZoom Level 4.5 extension:
Check and tell if its working.