Element Size Rules by VilleKokkarinen
Create reusable per-site CSS rules with a visual element picker and parent/child selector controls.
Available on Firefox for Android™Available on Firefox for Android™
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Extension Metadata
About this extension
Element Size Rules lets you customize the layout of websites with your own CSS. Create rulesets for specific sites or pages, choose elements with the visual picker, and adjust the selected element’s parent or child before saving.
- Match rulesets to pages using wildcard URL patterns.
- Add CSS manually or pick an element to create a selector.
- Edit, enable, disable, or delete rules and rulesets.
- Start with the included YouTube “4k” sample ruleset, and customize or remove it.
Rules are stored with Firefox Sync and may sync across devices when add-on syncing is enabled.
- Match rulesets to pages using wildcard URL patterns.
- Add CSS manually or pick an element to create a selector.
- Edit, enable, disable, or delete rules and rulesets.
- Start with the included YouTube “4k” sample ruleset, and customize or remove it.
Rules are stored with Firefox Sync and may sync across devices when add-on syncing is enabled.
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Permissions and data
Required permissions:
- Access browser tabs
- Access your data for all websites
Optional permissions:
- Access your data for all websites
Required data collection, according to the developer:
- Browsing activity
More information
- Add-on Links
- Version
- 2.0.5
- Size
- 42.23 KB
- Last updated
- 7 days ago (Sep 24, 2026)
- Related Categories
- License
- MIT License
- Version History
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