Firefox 78 for developers
This article provides information about the changes in Firefox 78 that will affect developers. Firefox 78 was released on June 30, 2020.
See also New in Firefox 78: DevTools improvements, new regex engine, and abundant web platform updates on Mozilla hacks.
Changes for web developers
- You can now change the URL accessed by the remote device from the about:debugging panel. (Firefox bug 1617237)
- Logpoints can map variable names in source-mapped code back to their original names, if you enable Maps in the Scopes pane. (Firefox bug 1536857)
- In the Network Monitor, you can now resize the columns of the request list by dragging the column borders anywhere in the table. (Firefox bug 1618409)
- The request details panel in the Network Monitor has some UX improvements. (Firefox bug 1631302, Firefox bug 1631295)
- If a request was blocked, the request list now shows the reason, such as an add-on, CSP, CORS, or Enhanced Tracking Protection. (Firefox bug 1555057, Firefox bug 1445637, Firefox bug 1556451)
- The Accessibility inspector is out of beta. You can use it to check for various accessibility issues on your site. (Firefox bug 1602075)
- Uncaught promise errors now provide all details in the Console, including their name and stack. (Firefox bug 1636590)
:where()pseudo-classes are now enabled by default (Firefox bug 1632646).
:read-writepseudo-classes are now supported without prefixes (Firefox bug 312971).
- In addition,
:read-writestyles are no longer applied to disabled
<textarea>elements, which was a violation of the HTML spec (Firefox bug 888884).
- In addition,
Intl.ListFormatAPI is now supported (Firefox bug 1589095).
Intl.NumberFormat()constructor has been extended to support new options specified in the Intl.NumberFormat Unified API Proposal (Firefox bug 1633836). This includes among other things:
- Support for scientific notations
- Unit, currency and sign display formatting
RegExpengine has been updated and now supports all new features introduced in ECMAScript 2018:
- Due to a WebIDL spec change in mid-2020, we've added a
Symbol.toStringTagproperty to all DOM prototype objects (Firefox bug 1277799).
- The garbage collection of
WeakMapobjects has been improved.
WeakMapsare now marked incrementally (Firefox bug 1167452).
ParentNode.replaceChildren()method has been implemented (Firefox bug 1626015).
- Extended Support Releases (ESR): Firefox 78 is the first ESR release that supports Service workers (and the Push API). Earlier ESR releases had no support (Firefox bug 1547023).
- Wasm Multi-value is now supported, meaning that WebAssembly functions can now return multiple values, and instruction sequences can consume and produce multiple stack values (Firefox bug 1628321).
- WebAssembly now supports import and export of 64-bit integer function parameters (i64) using
TLS 1.0 and 1.1 removal
- Support for the Transport Layer Security (TLS) protocol's version 1.0 and 1.1, is dropped from all browsers. Read TLS 1.0 and 1.1 Removal Update for the previous announcement and what actions to take if you are affected (Firefox bug 1643229).
Changes for add-on developers
browsingData.removePluginDatanow support deleting by hostname. (Firefox bug 1636784).
- When using
proxy.onRequest, a filter that limits based on tab id or window id is now correctly applied. This could be useful for add-ons that want to provide proxy functionality just in just one window.
- Clicking within the context menu from the "all tabs" dropdown now passed the appropriate tab object. In the past, the active tab was erroneously passed.
- When using
downloads.downloadwith the saveAs option, the recently used directory is now remembered. While this information is not available to developers, it is very convenient to users.
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