Install from the Chrome Web Store
Each of the four opens the Chrome Web Store and installs from it. There is no separate listing because there is no separate build.
All four are Chromium underneath and install Chrome Web Store extensions unchanged. Latr is the same package in each: close a tab with a time, and the page reopens on its own, where you stopped reading.
Why one package
Brave, Vivaldi, Opera and Arc are built on Chromium, the open-source core of Chrome. Chrome extensions run in them without changes, and that is the one Latr ships.
Each of the four opens the Chrome Web Store and installs from it. There is no separate listing because there is no separate build.
Snooze, reminders, the Open tabs screen, saved windows with their groups, the library, the focus timer, nine languages. Nothing is cut for a non-Chrome browser.
The install dialog asks for nothing alarming. Tab access and bookmarks are requested only when you open the screen that needs them, in every one of these browsers.
Browser by browser
None of these change how Latr works. They are the habits of each browser that meet it.
brave://extensions Shields leave Latr alone: a free install makes no network requests, so there is nothing to block. Brave’s own “tab snooze” is not a feature; this is where it comes from.
vivaldi://extensions Tab stacks are Vivaldi’s own; a saved window keeps Chromium tab groups, which Vivaldi shows as stacks. Latr’s side panel opens as a panel beside Vivaldi’s.
opera://extensions Opera installs Chrome Web Store extensions directly (it may ask once to allow the store). Workspaces stay Opera’s; the queue and library are the same in every workspace.
Menu → Extensions Arc auto-archives tabs. A Latr reminder is not a tab, so it survives the archive and reopens on time - the one thing Arc’s own archive cannot do.
The keyboard shortcut lives in the browser, not in Latr. Each of these has its own shortcuts screen under the extensions page, and the suggested key, AltShiftY, may already belong to something else there. Set it once and the fastest way to save a tab is one keystroke in any of the four.
Firefox is the one browser with a different package - an event page rather than a service worker, and notifications without buttons. The Firefox page has the two differences; Edge takes the same Chromium package as these four, from its own store.
Questions
Yes. Brave runs Chrome Web Store extensions, so install Latr from the Chrome Web Store and it behaves exactly as it does in Chrome. Brave Shields do not interfere: a free install of Latr makes no network requests at all, so there is nothing for Shields to block.
Yes, from the Chrome Web Store. One thing to know: Arc archives tabs it thinks you have abandoned after 12 hours, a day or a week. A reminder Latr holds is not a tab, so it survives Arc’s archiving, and the page reopens on time whatever happened to the tab it came from.
Yes, both install it from the Chrome Web Store. Vivaldi’s tab stacks and Opera’s workspaces are the browser’s own; Latr’s saved windows keep Chromium tab groups, which both browsers support, and the queue, library and focus timer work the same everywhere.
None of them has a store of its own for extensions; each one points its users to the Chrome Web Store. Opera has an add-ons catalogue, but it also installs Chrome extensions directly, and keeping a second copy of the same package in a second store would only let the two drift apart.
The package is built and tested on Chrome, and it is the identical file these browsers install; they add nothing and remove nothing from the extension APIs it uses. If something behaves differently in one of them, the support page is the place to say so.
In each browser’s own extensions screen, under “Keyboard shortcuts”: brave://extensions/shortcuts, vivaldi://extensions/shortcuts, opera://extensions/shortcuts, and in Arc through the Extensions entry in its menu. The suggested key is Alt+Shift+Y, and the browser may have given it to something else.
Free, no account, and nothing leaves your device. About ten seconds to install, and one keystroke to use.
Also on Brave, Vivaldi, Arc and Opera - straight from the Chrome Web Store listing.