Firefox may import data directly from Opera GX: first check Settings > Import Data. If Opera GX is not listed, export bookmarks from Opera GX as an HTML file and import that file into Firefox. Passwords use a separate CSV route, and whether Firefox can import that file depends on the options in your installed version.
Try Firefox’s Import Data wizard first
- Open Firefox and go to Settings > Import Data. The wording or location may differ by Firefox version. You can also open the Bookmarks Library and choose Import and Backup > Import Data from Another Browser, as Mozilla documents in its browser import instructions.
- Look for Opera GX in the list. If it appears, select the matching profile and review the data categories Firefox offers before importing. Available browsers and categories depend on what Firefox detects and supports; Mozilla does not explicitly guarantee that Opera GX will appear.
- When the import finishes, check the transferred items in Firefox before changing or removing the Opera GX profile.
The wizard’s categories are specific to the detected source. Do not assume it will bring over every part of a browser profile.
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If Opera GX isn’t listed, move bookmarks with an HTML file
- In Opera GX, open the bookmarks manager and use its export option to save bookmarks as an HTML text file. Opera documents this option in its Features help page.
- In Firefox, open the Bookmarks Library and choose Import and Backup > Import Bookmarks from HTML. Select the file exported from Opera GX. Mozilla describes HTML import as the fallback for bookmarks from a browser that is not listed in the import wizard in its import instructions.
- Check a few folders and important bookmarks in Firefox. If you are moving between devices, transfer the HTML file to the device running Firefox and import it there.
Use HTML for moving bookmarks between browsers. Firefox’s JSON or JSONLZ4 bookmark backup is intended for restoring Firefox bookmarks, not as the cross-browser transfer file; see Mozilla’s bookmark export and transfer guidance.
Handle saved passwords separately
Opera documents exporting saved passwords to a CSV file in its Web preferences help page. Firefox’s import documentation describes password import for supported sources and points to password-file import instructions. If Opera GX is absent from the wizard, check whether your Firefox version offers password import from CSV, then use that option if available.
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- Keep the CSV file private: it contains sensitive login information. Do not leave it in a shared or public location.
- After importing, verify several important logins in Firefox. The cited vendor instructions do not guarantee that CSV password imports work identically across every Firefox version and platform.
- Remove the exported CSV when you no longer need it, using a method appropriate for your device and storage.
What may not transfer
The documented fallback covers bookmarks and a separate password-file path. It does not establish that browsing history, extensions, cookies, settings, open tabs, or every other Opera GX profile item can be moved to Firefox through these steps. Expect to configure unsupported items manually. Mozilla’s backup, recovery, and sync guidance covers Firefox data management, but it does not establish a complete Opera GX profile migration.
Quick Recap
Choose the route that fits your setup
| Route | When to use it | Data and limits |
|---|---|---|
| Firefox Import Data wizard | Try first when Opera GX is on the device running Firefox and appears in the source list. | Imports only the categories Firefox offers for the detected source; Opera GX’s availability is not guaranteed. |
| HTML bookmark file | Use when Opera GX is not listed, or when you need to move bookmarks between devices. | Transfers bookmarks. Export from Opera GX and import the file into Firefox; it does not transfer the full profile. |
| Password CSV | Use as a separate option if the installed Firefox version provides CSV password import. | Opera documents CSV export, but compatibility varies by Firefox version and platform; verify entries after import. |
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