These notes are aimed at Firefox for the desktop (as opposed to mobile phones).
Download an installer and run it. Full off-line installers for various systems and languages can be downloaded from here. Older versions can be downloaded from here but that is strongly discouraged.
Before installing Firefox, you may want to first check the latest release notes or all release notes to find out about recent changes and fixes.
User Agent text when submitting a bug report,
do or
go to about:support.)
Sometimes Web browsers get bogged down, often (always?) because of a poorly designed Web site, possibly with memory leaks in the JavaScript code. The problem can usually be fixed by closing an offending tab, if you can identify it.
See Isolated Web Content for a long thread about one set of symptoms, including
a message about using about:processes in the address bar to identify
the problem. There is a follow-up message about
other about: features.
Some settings are accessible by typing
about:preferences in the URL bar and pressing
the Enter key,
or by doing
in Linux or
in MS Windows.
More advanced preferences are accessible by typing
about:config in the URL bar and pressing
the Enter key. A warning message may need to be acknowledged.
Click on to see the very long complete
list of settings, or use the
box to filter the list.
See also
Configuration Editor for Firefox for instructions;
about:config
for more detail,
about:config_entries
‘where the most important about:config variables
are described; and
http://kb.mozillazine.org/Category:Preferences
for a longer (but still not complete and up-to-date) list.
See also
Customizing Firefox Using policies.json
for administrators configuring Firefox across multiple computers.
After installation, you may want to do some or all of the following.
Downloads):.xlsx seems to be missing for some reason),
once such a file has been downloaded,
right-click the download in the
list and
choose
about:preferences#general
,
select
and make sure
is unchecked
about:config: set dom.disable_window_move_resize
to true.
about:config:
the default value of
browser.cache.check_doc_frequency
is 3 (Check for a new version when the page
is out of date), in some cases a better choice may be 1
(Check for a new version every time a page is loaded)
about:config:
the default value of dom.disable_window_open_feature.menubar
is false.
Changing it to true prevents this, thus allowing
one to, for example, access the print command in such a window.windowFeatures parameter
of window.open() can no longer control the visibility
of each UI part separately, but become a condition for
whether to open a popup or not (bug
1507375).’
I’m not sure what is meant by a ‘popup’.
This change may have made
dom.disable_window_open_feature.menubar unnecessary,
but it was still present in Firefox 78. I don’t know when
it disappeared.
about:config:
set devtools.hud.loglimit.
This used to be devtools.hud.loglimit.console and
apparently it changed sometime between Firefox versions 60 and 68
(based on searches with
searchfox.org).
/home/username/.mozilla/firefox/ (Linux)
c:/Users/username/AppData/Roaming/Mozilla/Firefox/Profiles/ (Windows 7)
To have desired settings on different computers, or after reinstalling an operating system, see information about profiles:
‘Because your preferences and extensions often cause problems, this article does not explain how to copy these between profiles’
Of the many available add-ons, these are ones that I have installed:
virtualboxes.org
was making 1000’s of calls to
JetpackLikesWidgetQueueHandler (this seemed to
be the worst offender), and leaving tabs open at google.ca or
maps.google.ca meant that JavaScript stuff
was running continuously in the background. This add-on stopped working
as of Firefox 33 because of a change in the debugging API, but
a
new version was released on 2015 Jun 11. The new version monitored
only the currently open tab.
The add-on again stopped working as of Firefox 57.
Some of its functionality is now provided by about:performance
in Firefox.
With version 57 (Quantum) a lot of things changed (ref), including a new multi-process core engine (Electrolysis), a new CSS engine (Stylo), a new GUI (Photon), and the dropping of support for the legacy XPCOM- and XUL-based extension systems in favour of the WebExtension API copied from Google Chrome (ref).
The user interface can now be customized using a file
chrome/userChrome.css in the user's profile
directory (see about:profiles).
Instructions and examples abound
(e.g.,
UserChrome.css at mozillaZine;
userchrome.org).
Similarly, the appearance of Web pages can be customized using
userContent.css.
Starting with Firefox 69,
toolkit.legacyUserProfileCustomizations.stylesheets must be
set to true in about:config
for userChrome.css and userContent.css to work.
(The @namespace line is sometimes said to be required but is
omitted by many (refs 1,
2).
CSS code can be added directly into user*.css or
invoked using @import
(ref).
The status bar at the bottom of the window now only shows up transiently.
userChrome.css is intended to make it permanent
(ref). I haven’t made it work yet.
Firefox now comes with a stupidity called Pocket. There are two aspects of it, which need to be disabled separately (ref):
about:config, set extensions.pocket.enabled
to false.
Many interface changes arrived with version 29 (Australis). One of the big debates was about whether tabs should be on top or on the bottom; they had been on the top by default for a long time but until version 29 there was a built-in method of moving them to the bottom. The delineation of the tabs also changed from straight lines to curves. To undo some of the interface changes, one option was the Classic Theme Restorer add-on. This add-on doesn't work in Firefox 57+.