Welcome to the XBMC forums, DarkRev2001.
You can install the Advanced Launcher add-on and use it to launch a web browser, such as Chromium or Firefox, from within XBMC. To install Advanced Launcher, on the XBMC homepage: System > Settings > Add-ons > Get Add-ons > XBMC.org Add-ons > Program Add-ons > select Advanced Launcher > Install.
As Vampirebat mentioned, Chromium is installed by default. You can install Firefox by going to the XBMCbuntu desktop (see Vampirebat's post) and selecting the Start menu > System Tools > Synaptic Package Manager. Enter your log-in password and in Synaptic Package Manager, search on firefox, select the firefox package, mark it for installation, and select Apply.
To setup Advanced Launcher to run a web browser (Firefox, in this example):
- On XBMC homepage, select PROGRAMS
- Select Advanced Launcher
- On the "Launcher Type" pop-up, select "Standalone (normal PC executable)"
- On the "Select the launcher application" pop-up, select "Root filesystem"
- Scroll down to "usr" and press Enter
- Scroll down to "bin" and press Enter
- Scroll down to "firefox" and press Enter
- On the "Application arguments" text-entry pop-up, blank out the prefilled text and click Done
- On the "Set the title of the launcher", accept the prefilled text (e.g., "firefox") or enter your own title (e.g., "Launch web browser") and click Done
- Close/cancel the remaining pop-ups that are presented ("Select the platform"; "Select Thumbnails path"; "Select Fanarts path")
- This completes the setup of your web browser launcher; now, exit back to the XBMC homepage to test it
To launch your web browser while in XBMC:
- On the XBMC homepage, select PROGRAMS
- Select Advanced Launcher
- Select the web browser launcher entry you created above (e.g., "Launch web browser")
- XBMC is reduced from fullscreen to a smaller window and your web browser is launched
- When you are done with your web browser, simply close it and your XBMC session will be restored to fullscreen