This epic will track the work that is required to rebase Firefox ESR packages in RHEL from version 115 to 128. For the common information (i.e. schedule) about Firefox ESR and Thunderbird rebases see the parent feature - RHELBU-2535. Process related tasks are tracked in DESKTOP-821.

Summarized changelog - for more information please look at https://en.wikipedia.org/wiki/Firefox_version_history#Firefox_115_through_127 and changelog for 128 release itself:

• Firefox 116 was released on August 1, 2023. Major changes included the sidebar switcher allowing users to access Bookmarks, History and Synced Tabs panels easily, quickly switch between them, move the sidebar to another side of the browser window, or close the sidebar; available access to the release notes in the update notification prompt in the form of a "Learn More" link whenever an update is available in English locales; the ability for users to copy any file from their operating system and paste it into the browser; the volume slider in Picture-in-Picture; the possibility to edit existing text annotations; the improvement of the upload performance of HTTP/2 on those with a higher bandwidth delay product; added support for the dirname attribute to pass text directionality information about input and textarea elements to the server; added support for CSP3 external hashes; the Audio Output Devices API that now enables sites to redirect audio from media elements to permitted output devices (speakers) other than the system default for the user-agent; added upport for proper BYOB readers on Fetch and WebTransport, which allows developers to prepare their ArrayBuffer so that it can be reused for read requests and thus saves memory allocation.

• Firefox 117 was released on August 29, 2023. Major changes included the extension of support for credit card autofill to users running the browser in the IT, ES, AT, BE, and PL locales; the addition of a dom.event.contextmenu.shift_suppresses_event preference to prevent the context menu from appearing; the browser no longer showing its own screen sharing indicator on Wayland desktop environments; the enhancement of web compatibility inspection with the new CSS compatibility tooltip in the Developer Tools Inspector; added support for improved CSS nesting by default; support for RTCRtpScriptTransform, ReadableStream.from (allowing creation of a ReadableStream from an (async) iterable), and the math-style and math-depth CSS properties and the font-size: math value.

• Firefox 118 was released on September 26, 2023. Major changes included the introduction of automated translation of web content, courtesy of the EU-funded Project Bergamot; the use of the FDLIBM math library on all systems to improve anonymity with Fingerprint Protection via web audio in the browser; the restriction of visibility of website fonts to system fonts and language pack fonts to mitigate font fingerprinting in Private Browsing windows; the availability of Video Effects and background blur on Google Meet; the ability for U.S. Firefox Suggest users to see browser add-on suggestions right in the address bar based on their keywords; support for CSS math functions round, mod, rem, pow, sqrt, hypot, log, exp, abs, and sign; OpaqueResponseBlocking enabled by default.

• Firefox 119 was released on October 24, 2023. Major changes included the addition of Firefox view and the PDF editor; recently closed tabs now persisting between sessions that don't have automatic session restore enabled; the ability to import extensions from Google Chrome; support for the partitioning of Blob URLs, which mitigates a potential tracking vector that third-party agents could use to track an individual; the restriction of the visibility of website fonts to system fonts and language pack fonts in Enhanced Tracking Protection strict mode to mitigate font fingerprinting; an update to the Storage Access API to improve security while mitigating website breakages and further enabling the phase out of third-party cookies in the browser; the addition of Encrypted Client Hello (ECH), which extends the encryption used in TLS connections to cover more of the handshake and better protect sensitive fields; media sniffing no longer being applied to files served as type application/octet-stream; the ability for the mouse pointer to disappear while typing if the relevant Windows mouse properties system setting is enabled; the inclusion of the Santali (sat) language; a fix for an issue causing unexpected jumps in scroll position on Facebook; several enhancements to the Inactive CSS styles feature, which assists in identifying CSS properties that have no effect on an element; the automatic switch to a raw data view if the JSON is invalid or broken; added support for ARIA reflection for simple attributes and default Accessibility Semantics for Custom Elements; added support for credentialless in Cross-Origin-Embedder-Policy; added CSS attr() function for a fallback parameter; easier grouping of items by using the methods Object.groupBy or Map.groupBy

• Firefox 120 was released on November 21, 2023. Major changes included added support for a new "Copy Link Without Site Tracking" feature in the context menu which ensures that copied links no longer contain tracking information; added support for a setting (in Preferences → Privacy & Security) to enable Global Privacy Control and inform websites that the user doesn't want their data to be shared or sold; the enhancement of the Canvas APIs with Fingerprinting Protection for the browser's private windows and ETP-Strict privacy configuration for the protection of users' online privacy; the enabling of Cookie Banner Blocker and URL Tracking Protection by default in private windows for all users in Germany; the import of TLS trust anchors (e.g., certificates) from the operating system root store; the addition of keyboard shortcuts for editing and deleting a selected credential on about:logins; added support for corner snapping on Windows and Linux for Picture-in-Picture; the addition of the User Activation API, which allows servers to send resource Link headers before the final HTTP response and improves performance on servers using this feature; the ability for users to use an added devtools feature to simulate browser tabs to be offline; the Style Editor panel's feature of a new "Pretty Print" button located in the footer of the panel, similar to the pretty print button found in the Debugger panel, used to format stylesheets (e.g., those that are minified); the Rules panel within the inspector panel no longer displaying colors in the new CSS Color 4 formats (e.g., OKLCH) as hexadecimal/named colors, ensuring that it matches the original values used; the ability for lh and rlh units to be parsed and computed correctly as lengths; the enabling of WebAssembly GC by default, which allows new languages, such as Dart or Kotlin, to run on the browser

• Firefox 121 was released on December 19, 2023. Major changes included a default to the Wayland compositor when available instead of XWayland for Linux users; the ability to force links to always be underlined, which can be enabled in the Browsing section of the Settings menu; the floating button in the PDF viewer to simplify deleting drawings, text, and images added in PDFs; the Firefox Debugger including a new feature: an option to disable the debugger; keyword on the current page; the unification of the focus indicator across the toolbox, which is now larger with improved contrast, featuring a white box-shadow for enhanced visibility on blue backgrounds; added support for the :has() selector, which authors to match an element that has, or "anchors", at least one element matching its relative selector; added support for the hanging and each-line keywords for the text-indent CSS property, offering more convenient paragraph layout options for styles such as bibliographies, poetry, etc.; added support for the balance keyword for the text-wrap CSS property, which can improve the appearance of short multi-line text blocks such as long headings or captions by harmonizing the line lengths; added support for the lazy loading iframes, which are only loaded when visible, so non-critical iframes can load later when needed to speed up initial page loads, reduce initial network usage, etc.; added support for tail call elimination in WebAssembly language to improve support for functional languages

• Firefox 122 was released on January 23, 2024. Major changes included new displays of images and descriptions for search suggestions when provided by the search engine; improvement in the quality of translated webpages in the translations feature; the availability of MDN Web Docs article suggestions from Firefox Suggest in the address bar for users searching for web development-related information; the line breaking rules of Web content matching the Unicode Standard, improving Web Browser compatibility for line breaking; a fix for keyboard navigation in Inspector Rules view; enabled offset-position property which is useful for most of the offset-path values; added support for ray(), basic-shape and coord-box to the offset-path CSS property; added support for rect() and xywh() basic shapes on clip-path and offset-path CSS properties; added support for animating the SVG viewBox attribute using SMIL by animations; LargestContentfulPaint API, which provides timing information about the largest image or text paint before users interact with a web page; added support for hr in select, allowing websites to easily use separators inside a select element; added support for the showpicker method on <select> elements; the fallback URL parser for unknown schemes changed to DefaultURI, improving specification adherence and web compatibility; the ArrayBuffer.prototype.transfer proposal methods, which enables transferring ownership of ArrayBuffer data; added support for the Screen Wake Lock API; recognition of the "webauthn" autocomplete token; the ability for scripts to store cacheAPI data in Private Browsing mode; the tainting of filters that use currentColor as an input to further protect user privacy; Uneven Level Protection Forward Error Correction (ULPFEC) turned on by default.

• Firefox 123

• Firefox 124

• Firefox 125

• Firefox 126

• Firefox 127

• Firefox 128

For even more summarized changelog between 115 and 128 take a look at https://www.mozilla.org/en-US/firefox/128.0esr/releasenotes/ (when ready).