(NOTE)
Current policy: <https://www.mediawiki.org/wiki/Compatibility#Browsers>
* Affected components: MediaWiki core, skins and extensions.
* Stakeholders:
** #readers-web-backlog
** Product managers
** #traffic
### Motivation
* Persist / possibly improve user experience by enabling skin interfaces using of `rem` units, making them fully text zoomable by users with accessibility needs and do away with pixel based text and image sizing
* Simplify design–development handover by doing away with close to incomprehensible `em` based sizing
See {T262928} for more information on the negative effects of somewhat sticking to `em`s.
Note that the reality of supporting Firefox 3.0+ in MediaWiki core was not fully reflected for a while any more.
[[ https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/3.5 | Firefox 3.5 was the first version ]] to include crucial rendering and interaction properties like
- media queries,
- full `::before` and `::after` support
- `opacity` instead of `-moz-opacity` property
which have been widely used in core.
[[https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/3.6 | Firefox 3.6]] on the other hand has introduced `rem` support and additionally from the more often used properties `background-size` or `pointer-events`.
### Proposal
I'm proposing to **bump Firefox to at least v3.6+ in “Basic” in the [[ https://www.mediawiki.org/wiki/Compatibility#Browser_support_matrix | browser support matrix ]]**. It was released Jan 21, 2010.
This would be effective in MediaWiki 1.36, released later this year.
##### Statistics
Turnillo shows that use of Firefox 1-3 is approximately 580K per week across the wikis, with no particularly high usage in any given country. While this includes version 3.6 and falls well below the [[ https://phabricator.wikimedia.org/T262946#6510278 | 1% threshold ]] applied to other such decisions before, we've found out in process, that Wikimedia wikiprojects are limited to TLS 1.2+ since Jan 2020, see T238038 and therefore isn't accessible at all any more for Firefox lower than 27, including Firefox 3.