I couldn't zoom web pages in Internet Explorer using ctrl ++ and ctrl --, Why?

Because Ctrl ++ and Ctrl -- are short cut keys of Firefox. Using which you can zoom in or zoom out a web page only if your browser is Firefox.

OK, How to zoom web pages in Internet Explorer?

You have 5 options

View -> Text size -> smallest

Or

View -> Text size -> smaller

Or

View -> Text size -> medium

Or

View -> Text size -> largest

Or

View -> Text size -> larger

Select either one to zoom in or zoom out. Is it enough Mr. Cool?

Tell me how to zoom a web page in Firefox? Is there any way to increase the font size of a website?

Zoom is the right word I can use.

A web page can be zoomed very easily in Firefox.

Press Ctrl ++ to zoom in

Press Ctrl -- to zoom out