Explain how Firefox uses user profiles

This extends the Firefox profile documentation by explaining how
Selenium works when supplying an existing profile directory. Since
profiles are not cleaned up by Selenium, it also describes how they can
be explicitly removed by the user.

Author: Ozoniuss

Diff for: website_and_docs/content/documentation/webdriver/browsers/firefox.en.md

@@ -135,7 +135,16 @@ options.profile = FirefoxProfile()
 driver = FirefoxDriver(options)
   {{< /tab >}}
 {{< /tabpane >}}
-
+**Note**: Whether you create an empty `FirefoxProfile` or point it to the directory of your own profile, Selenium
+will create a temporary directory to store either the data of the new profile or a copy of your existing one. Every
+time you run your program, a different temporary directory will be created. These directories are not cleaned up
+explicitly by Selenium, they should eventually get removed by the operating system. However, if you want to remove
+the copy manually (e.g. if your profile is large in size), the path of the copy is exposed by the `FirefoxProfile`
+object. Check the language specific implementation to see how to retrieve that location.
+
+If you want to use an existing Firefox profile, you can pass in the path to that profile. Please refer to the official
+[Firefox documentation](https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data#w_how-do-i-find-my-profile)
+for instructions on how to find the directory of your profile.
 
 ## Service
 

Diff for: website_and_docs/content/documentation/webdriver/browsers/firefox.zh-cn.md

@@ -139,6 +139,16 @@ driver = RemoteWebDriver(options)
 {{< /tabpane >}}
 </div>
 
+**Note**: Whether you create an empty `FirefoxProfile` or point it to the directory of your own profile, Selenium
+will create a temporary directory to store either the data of the new profile or a copy of your existing one. Every
+time you run your program, a different temporary directory will be created. These directories are not cleaned up
+explicitly by Selenium, they should eventually get removed by the operating system. However, if you want to remove
+the copy manually (e.g. if your profile is large in size), the path of the copy is exposed by the `FirefoxProfile`
+object. Check the language specific implementation to see how to retrieve that location.
+
+If you want to use an existing Firefox profile, you can pass in the path to that profile. Please refer to the official
+[Firefox documentation](https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data#w_how-do-i-find-my-profile)
+for instructions on how to find the directory of your profile.
 
 ## Service