A collection of things I've learned that I think others might like to know, but aren't big enough to fill a whole page all their own.
#include_next — search for an include file that isn't the 
current one.  Allows you to extend system headers (e.g. to provide 
compatibility shims).printf("%*s", 32, "foo") — use one argument as padding width 
for another.printf("%.10s", ...) — print up to 10 bytes from the given 
string (allows printing w/o null terminator).printf("%.*s", (int)len, buf) — print a non-null-terminated 
string.You can double click to select a full word in most GUI applications — but it turns out if you keep the mouse held after the second click, and drag, you can make a larger selection that still only contains full words.
F3 will open a command palette.-Sres:1080 URL to download the best quality video no larger 
than the given vertical resolution.--term-title can do ternary operators, not just individual 
properties (e.g. ${?pause==yes:⏸ }${?pause==no:♫} 
${media-title}).g<C-a> — in visual mode, increment the first number on 
each line of the selection, with the amount added increasing by one each 
time.C-x s — switch to a mode where individual keys do commands 
(s to step, c to continue, etc.)In Firefox, you can right click the URL bar for many websites to add their 
search page.  This can then be set as the default, or given a custom shortcut 
under Settings > Search > Search Shortcuts, so that by typing 
@foobar<Tab> in the navigation bar you can search that 
website.  For example, I have search shortcuts for the following:
For sites this doesn't work on, there's an extension:
CTRL-B — Open bookmarks side panel.CTRL-D — Bookmark current page.CTRL-D ALT-R — Delete bookmark (if current page is 
bookmarked).