See these support articles:

• https://support.mozilla.org/kb/using-tabs-app-tabs-and-tab-groups
• https://support.mozilla.org/kb/what-are-app-tabs
• https://support.mozilla.org/kb/what-are-tab-groups

If you pin a tab then you move this tab to the left end of the Tab bar where it becomes a small tab the only shows the favicon if there is one available (no text).

Here are some more;

http://www.bing.com/search?q=Firefox%20-%20MakeUseOf%20Manual.com&qs=n&sk=&form=BDKTMS&pc=BDT3&shash=&BDParam=0000&mkt=en-US

keeshui said

So no technical question (yet), just a bit problems with my learning curve how to use firefox and his or hers functionallity(s) with more pleasure and faster then to often by try and find out (and to often loosing then again a lot of where i already was or came). for example now what does pin a tab i don't find and i assume/know i need it and after try and find out maybe i know after playing a whole evening or day with un- and pin but i would have preferred then, just type in "pin" somewhere and read basics about it. Am I to lazy or slow ?

Thanks; Chosen solution at least learned me a bit new words/names (, and that a lot of links here link to this same page back as i'm on now ). When i have time i'm going to visit/explore/?contribute/learn your site more.