Preferences are the seventy or so user options for browsing, editing, searching, notifications, and more. A link to your Preferences page is available at the top of every Wikipedia page when you have an account, alongside links to your other account services such as your Contributions. Another way to get there is by navigating to the Special:Preferences page.
Once at your Preferences page, you can control much of the Wikipedia user interface through the many feature settings provided by MediaWiki (the software of Wikipedia): skins, plug-ins, date formats, a signature, and more. For example, you can select to be prompted to enter an edit summary if you forget to. The Preferences page also presents a link to customize your CSS to adjust your page style details.
At their site, MediaWiki maintains a browser compatibility matrix. The time you spend in getting an account, setting your preferences, finding tools and testing your browser (before you ever lose an edit) will pay off.
Feature requests can be made, and bugs reported, as described at Wikipedia:Phabricator. The current set of preferences are largely the result of issues raised by newcomers at places such as the Village pump, and driven by regulars who hold long discussions and collectively drive issues.
You do not need to click Save on every tab on the Preferences page, as the Save button affects all changes on all Preferences tabs. You can go from tab to tab setting all your preferences before saving, because Save remembers your changes on the other tabs. To forget unsaved changes, simply leave the page without saving. If you wish to undo your saved changes, you will need to reset them manually.
The default settings are aimed at newcomers editing articles. Intermediate editors tend to activate more features, such as "warn me if I forgot an edit summary", and advanced editors and administrators use the special settings, gadgets and editors for their tasks.
If you have chosen to make your Wikipedia login a global account, you will have the same username and password on Sister projects such as Wiktionary, at MediaWiki.org itself, and on the Wikipedia of other nations. Each of your account's preferences are independent because each wiki is a website, with their own administration (namespaces, settings, accounts, etc.). Even the word "Preferences" on the top may be set differently! At Simple Wikipedia it says "My settings".
Lists your account details and some statistics.(e.g. number of edits)
Allows you to view/manage your global account info.
This is where you change your password.
Change the language of user-interface messages. It does not affect articles and other pages made by editors. Note that many interface messages have been customized at the English Wikipedia but usually only for the default "en - English" which may for example add links to relevant help pages, processes and policies. It is therefore not recommended to select "en-GB - British English" or "en-CA - Canadian English" which make a few spelling changes but omit many useful customizations. Foreign languages also omit customizations but may still be preferred by users with poor English abilities.
Option to specify your preferred pronoun in order for the software to grammatically refer to you correctly.
More language settings: allows you to set the language in which Wikipedia menus and fonts are displayed; additionally, an option to set the language you edit in (input tools must be enabled).
Displays the signature that will appear when you sign talk pages.
Allows you to edit the signature, either using wiki markup (the option must be checked), or just plain text.
Choose the "skin", or "theme" of how Wikipedia is displayed.
Option to set your date and time preferences; this is how dates will appear in article History pages, logs, etc. If set to "No preference", the format is HH:MM, DD MMMM YYYY (UTC), for example: 15:28, 15 December 2018 (UTC).
Shows the server time (UTC) and the local time based on the optional Time zone setting. You may opt to use the server time (UTC), have the offset calculated by the clock in your computer, or specify an offset from UTC in hours or by location.
The images in an article are just a thumbnail (a preview). These will always be one of eight possible Thumbnail sizes. For the larger screen sizes choose the maximum, and for the smaller screen sizes choose the minimum thumbnail size. The default 220px is a midrange thumbnail-size. Have you changed your font size? Then you should match that font size to your chosen thumbnail size to increase caption readability.
You can target the Image size limit of the file page main image, (displayed in the front matter). On a faster network choose a larger size, and on a slower network choose a smaller Image size limit. The default 800×600px is a midrange Image size limit. File pages are on Commons wiki, and if logged in there, going there overrides your settings here.
Note that you can both turn off Media Viewer and set a small Image size limit, and yet you will not limit your ability to avail yourself of any high resolution images listed at the bottom of that file page, when wanted. Doing so you can get full manual control of any unwanted, automatic bogging-down of your surfing speed caused by automated choices concerning File namespace interactions initiated by clicking on an image.
Option to not show page content below the diffs; checking this will suppress the page preview of the difference you're viewing.
Option to omit a diff after performing a rollback
Chose to display hyperlinks with underlines in your browser window always, never, or by browser or Wikipedia-skin default.
Format links as stub links when the article they link to is smaller than the threshold you set on file size. Stub link formatting changes the link color to the dark brown displayed in this option's text. This option can help you see links to small articles (more likely to be stubs) so that you might expand them. It is also useful for spotting links to disambiguation pages, which are also relatively small. They are usually linked to in error, but often contain on their list a link to the correct article, making this error easy to fix.
Concerning the edit page, its initiation, look and feel, Wikipedia offers a remarkable number of options. Some of them are:
"Prompt me when entering a blank edit summary" into the database. (Habit-forming.)
"Enable VisualEditor". Get a word processor interface. No markup language at all.
The font size for edit box can be set in Wikipedia editing preferences or in the browser. In Firefox there are two font-size settings at Options → Content → "Default font"Advanced..., one for the edit box, and one for the rest of the page. If you just want uniformity, check to see if it allows Wikipedia to choose its own font; then you set Wikipedia's "Edit Area Font Style" to "Serif" or "Sans Serif", and the font size in the edit box will match the rest of the page.
Two editing toolbars are offered that will span the top of the edit box. (Wikipedia:Reftoolbar shows versions.)
"Show edit toolbar" is the legacy 1.0 version that gives a row of buttons. (See m:help:Edit toolbar for details.)
"Enable enhanced editing toolbar" gives a frame with icons. It is a default feature that can be turned off.
Recent changes refer to changes of pages in the database. Every time a wiki page is edited, and changes were actually made, a record is kept of the difference. For example, a page history shows the revisions for that particular page. But recent changes can report on more than just the revisions of a page, or an entire wiki, they can also report on the recent changes of an editor (their contributions). The user preferences for recent changes are the style in which these lists of revisions will appear:
Length of the list
Time window of the list
Grouping methods of the list
The watchlist has even more finely tuned preferences, because like the edit window, it is often a core tool for editors.
These settings are for advanced editors who have a detailed understanding of the five pillars and of the templates used to mark judgments on the page. Pending changes refers to the style of the presentation of
The watchlist options include which pages, and what "recent" means to you.
If your Preferences has "Email me when a page or file on my watchlist is changed" set (at the bottom of the "User profile" tab), then only by visiting a page will you actually set its email notification flag.
Once you miss the email for a particular page change or don't visit the page (or ignore the email), you will not receive any more emails for that page. You can still dutifully monitor that page by its watchlist edit-summaries, but its particular email notification flag will remain unset until you visit it. This facilitates monitoring a large watchlist while preventing potentially useless emails to you.
In case you want to set all email notifications anyway, you can at any time mark all pages "visited". If your Preferences → Gadgets has "Display pages on your watchlist that have changed since your last visit in bold", then your watchlist will have a button labeled "Mark all pages visited". That button will effectively set all of your email notification flags.
Beta Features is a way for to test new features on Wikipedia and other Wikimedia sites before they are released for everyone.
The MediaWiki preferences page offers a set of options for the generic user. If you discover a special role on Wikipedia, there is probably a powerful tool for it at WP:Tools#Browsing and editing.
^The danger in using Live preview is on first use with an incompatible browser. Try a simple test: make a change to the edit box, then reload the page.