Handy keyboard shortcuts

Xfce desktop environment

Workspaces

CTRL + F1 (etc) switch to that workspace
alt + tab switch to the previous active window(works in pretty much any DE or window manager, and even Windows)
alt + f4 - close the active window
print screen - take a screenshot of the screen

Mozilla Firefox (on linux)

Most of the keyboard shortcuts will work on Windows too

CTRL + tab - select a tab with the arrow keys while holding.
CTRL + T - open a new tab

CTRL + D - book mark the current page

CTRL + W - close the tab

CTRL + L jump to the url bar

Home - top of the page (depending if something like a video is in focus)

End - End of the page (depending if something like a video is in focus)

CTRL + SHIFT + Y open the downloads menu

CTRL + SHIFT + O open the all book marks menu

Websites

Youtube

spacebar - pause video
j and l - j rewinds the video by 10 seconds l by 10 seconds
arrow keys – left arrow key rewinds the video by 5 seconds (to the right the other way)
up and down on the arrow keys raises the volume up and down.
C key - turn the subtitles on and off
home key - go to the beginning of the video