Most modern web browsers are capable of increasing/decreasing font sizes while on a webpage. For detailed instructions please see the WCAG documentation page.

To increase the font size, hold the Ctrl key (Command key on a Macintosh) and press the + (plus) key.

To decrease the font size, hold the Ctrl key (Command key on a Macintosh) and press the – (minus) key.

To revert to the default font size, hold the Ctrl key (Command key on a Macintosh) and press the 0 (zero) key.

You can also set font-sizes universally for all pages that you visit in some browsers.

For Internet Explorer, press the “Alt” key on your keyboard. A new menu will appear below the address bar, click “View” and select “Text Size”.

For Safari, click the “Safari” menu in the top-left corner of your screen, then select “Preferences”. Then click “Advanced” and check the “Never use font sizes smaller than” checkbox under “Accessibility”. Set this to your liking.

For Chrome, click the “Menu” icon at the top-right of your window (3 horizontal lines) and then select “Settings”. Scroll down and click “Show advanced settings”. Scroll down to “Web content” and adjust to your liking.

For Firefox, click the “Menu” icon at the top-right of your window (3 horizontal lines) and then select “Preferences”. Select “Content” from the left-sidebar. The “Fonts & Colors” section can be adjusted to your liking.

Most modern operating systems are capable of zooming your entire screen. This may be a good alternative if increasing font sizes alone is not sufficient.

For Windows, click the “Start” menu in the bottom-left corner of your screen and then go to “All Programs”, then “Accessories”, then “Ease of Access” and then click “Magnifier”. Click the “Options” button and then move the slider to adjust the zoom increment.
More information about Windows’ zoom accessibility features.

For Mac OS X, click the Apple menu in the top-left corner of your screen and go to “System Preferences”, then choose “Accessibility”, then click “Zoom”. You can assign keyboard shortcuts or trackpad gestures.
More information about Mac OS X’s zoom accessibility features.

Third party software is also available:
ZoomText
MAGic

Most modern web browsers allow you to override fonts with your own formatting.

For Internet Explorer, click the “Tools” button and then click “Internet Options”. Then click the “General” tab and then click “Accessibility”. Check the following checkboxes “Ignore colors specified on webpages”, “Ignore font styles specified on webpages”, and “Ignore font sizes specified on webpages”. Then click “Ok” and change the fonts to your liking.

For Internet Explorer, click the gear icon at the top-right of your window and then select “Internet Options”. Click the “General” tab and then click the “Colors” button under “Appearance”. Uncheck “Use Windows Colors” and change the colors to your liking.

For Chrome, install the Change Colors extension.

For Firefox, click the “Menu” icon at the top-right of your window (3 horizontal lines) and then select “Preferences”. Select “Content” from the left-sidebar. Click “Colors…” in the “Fonts & Colors” section and adjust the colors to your liking..

Lowering your screen resolution may help you keep track of your mouse cursor. Alternatively, most modern operating systems allow you to increase the size of your mouse cursor.

For Windows, click the “Start” menu in the bottom-left corner of your screen and then type “Mouse” (may need to click “Search” first if using Windows 8 or later). Select the “Mouse” option. Click the “Pointers” tab and adjust the size to your liking.

For Mac OS X, click the Apple menu in the top-left corner of your screen and go to “System Preferences”, then choose “Accessibility”, then click “Display”. Adjust the “Cursor size” slider to your liking.

Task Keys
Move forward through items on a page Tab
Move backward through items on a page Shift + Tab
Press a selected button Spacebar
Navigate radio buttons Arrow keys
Select and deselect checkboxes Spacebar
Open a dropdown menu Alt + Down arrow
Go to the previous tab Ctrl (or Cmd) + Page Up
Go to the next tab Ctrl (or Cmd) + Page Down
Go to the top of the page Home
Go to the bottom of the page End
Close the current tab or window Ctrl (or Cmd) + W
Refresh the page F5 or Cmd + R

More information about Windows accessibility features.
More information about Mac OS X accessibility features.
Accessibility extensions for Chrome
Accessibility add-ons for Firefox
Tips from W3C