I just figured this out and it is so convenient. I will show by example. I am using Firefox, but other browsers might work the same way.
(1) Go to lemmy.ml
(2) Ctrl+D, then enter to save as a bookmark
(3) Ctrl+shift+O to open the bookmark settings
(4) Select the lemmy bookmark that you just created
(5) At the bottom of the menu, you can set a Keyword. Write the letter "l".
(6) Close the menu
You can now type "Ctrl+L" to jump to the navigation bar, then type "l", enter.
You can create single or few-letter keywords for the sites that you visit often.
Bonus related tip: In the browser preferences, under "search", you can define a keword for specific search engines. For example, if you set wikipedia to "@w", you can then search directly from the navigation bar by typing "@w whatever"